Roasted Red Onions are an unexpected and amazing vegetarian side dish -- or an ingredient that can be added to dozens and dozens of recipes. The slow roasted onions transform from raw, firm and sharp, to sweet, soft, and aromatic.
It's always fun to present something that might be new to friends and family. Especially something like taking one simple ingredient and turning it into an amazingly special dish.
I cook onions nearly every day, though they are typically the foundation for a dish. However, these Roasted Red Onions are the dish. Whole roasted onions are a deeply flavored, subtly sweet vegetarian side dish.
The Ingredients
This recipe is really all about one everyday, simple ingredient. A red onion.
(I often suggest brands I love and use -- these are only suggestions, and this is not a sponsored post.)
- red onions - Choose onions that are heavy for their size and without bruises. For this recipe, we want very small red onions, about 5 to 6 ounces each.
- extra virgin olive oil - I use this one.
- fresh herbs (rosemary, thyme, oregano) - Look for perky bunches and avoid any brown, bruised or yellow leaves.
- butter - I always cook (and bake) with unsalted butter so I can control exactly how much salt is in the recipe.
- salt - I cook with Kosher salt. I prefer for a few reasons: its larger flake size, it's less refined and usually doesn't contain additives, and it does a great job enhancing the flavor of foods without making them taste salty.
- black pepper - Preferably freshly ground.
(See recipe card below for quantities.)
Substitutions
- You can use yellow or white onions for this recipe as substitutions for the red, if you prefer. The key is that they're not too big -- 5 to 6 ounces is ideal.
- I love the combination of rosemary, oregano and thyme with roasted red onions, but you can substitute, or use more or less of any of them. Marjarom or sage would both work well.
- If you want to keep the recipe vegan, substitute the butter with more of the olive oil.
How to Make Them
- Preheat the oven to 300°F, and adjust a rack to the center.
- Leaving the skin on, wash and dry the onions.
- With the skin still on, cut the root end off of each one, just about ½-inch, only enough to create a base. Then, slice about 1-inch off the top of each one, and use the knife to mark an “X” the surface, only cutting into it about ½-inch or so.
- Place them in a 9 x 13 x 2-inch pan, on their bases. Drizzle about 3 tablespoons of the olive oil on the flat surface of the onions -- over the "X." Sprinkle generously with salt and pepper and place them in the preheated oven for 1 hour.
- Remove them from the oven and drizzle with the remaining 2 tablespoons of oil. Cover the pan lightly with foil, return them to the oven for 1 more hour.
- Remove the onions from the oven again and take off the foil. Add about half of the fresh herb sprigs to the pan, surrounding, and on top of the onions.
- Evenly distribute the butter among the onions, on the top center of each one. Uncovered, return the onions to oven and roast for another 30 minutes.
- Baste the onions with the juices from the bottom of the pan and turn the heat up to 350°F.
- Continue to roast for 1 to 2 more hours, basting them every 20 minutes with more juices from the bottom of the pan. (It's your call -- the longer you roast, the more caramelized and soft they'll be.)
And for an even deeper flavor . . . when you turn the oven up to 350°F, peel and cut the onions into quarters from the "X" at the top.
- Remove from the oven and let them cool in the pan. If you haven’t already done so, when they’re cool enough to touch, take off the skins and slice. Serve with the remaining fresh herbs.
(More detailed instructions are in the recipe card below.)
Recipe Tips
- I add fresh rosemary, oregano and thyme on their sprigs, breaking them into pieces if they're extra long. If the leaves of the herbs are especially big, they can be roughly chopped.
- There are set cooking times in the recipe card below, but you don't have to be exact with them. The key is knowing that the longer they onions cook, the sweeter and softer they'll be.
- If at any point while the onions are uncovered they seem like they are becoming too dark (darker than golden), lightly cover them with foil.
- Cooking times may vary, depending on the size of the onions -- just be sure they're very, very soft when they're done.
- And a final tip, don't wash the baking dish right away, and use it to roast other vegetables, like carrots or potatoes. They'll soak up the leftover juices from the onions and be rich and delicious. If you're not going to use it right away, just cover it with foil and refrigerate until you do.
Serving Suggestions
- These whole roasted onions can be served on their own as a side dish. They're excellent served alongside Lavender-Rosemary Grilled Ribeye Steak, Rosemary Lamb Skewers, and Blackberry Butter Roasted Chicken. (You can either slice the onions or serve them whole, for a more dramatic presentation.)
- They can also be added to stews, rice dishes and how about mixed into scrambled eggs? (This is excellent, trust me!)
- Roasted red onions can become so soft that you can practically spread them on bread. Imagine a layer beneath mashed avocado. It's makes for an incredible avocado toast!
Other Delicious Onion Recipes
- Grilled Green Onions
- Lime Pickled Shallots
- The Best Caramelized Onions
- Tomato Onion Salad
- Braised Pearl Onions and Chestnuts
Making Them Ahead and Storage
- The onions are at the best when eaten the day, or day after they're made.
- They can be stored for about a week in the refrigerator in an airtight container.
- To reheat them, place them in baking dish and in a 375°F oven until hot.
- I do not recommend freezing them.
What happens to onions whey they're slow roasted?
Much like when we slow roast garlic, roasting onions for a long time at a low temperature softens them and slowly draws out the natural sugars as they cook, caramelizing them, almost from the inside out.
With no sugar added, roasted red onions are unbelievably sweet, and while they still taste like onions, they're incredibly mild.
I hope you find these roasted red onions to be as incredible as I do!
Roasted Red Onions Recipe
Equipment
Ingredients
- 10 small red onions (about 5 to 6-ounces each)
- 5 tablespoons extra virgin olive oil
- a few sprigs of fresh rosemary, thyme and oregano (washed and dried)
- 2 tablespoons unsalted butter
- salt and pepper
Instructions
- Set oven. Preheat the oven to 300°F, and adjust a rack to the center.
Prep Onions
- Leaving the skin on, wash and dry the onions. Then, with the skin still on, cut the root end off of each one, just about ½-inch, only enough to create a base so the onions don’t roll. Then, slice about 1-inch off the tip (top) end of each one, and use the knife to mark an “X” on the surface, only cutting into it about ½-inch or so. Place them in a 9 x 13 x 2-inch pan, on their bases.
- Drizzle about 3 tablespoons of the olive oil on the flat surface of the onions -- over the "X." Sprinkle generously with salt and pepper.
Roast the Onions
- Place in the preheated 300°F oven, uncovered.
- After 1 hour, remove them from the oven and drizzle with the remaining 2 tablespoons of oil, making sure it seeps into the "X." Now cover the pan lightly with foil and return them to the oven for 1 more hour.
- Remove the onions from the oven again and take off the foil. Add about half of the fresh herb sprigs to the pan, surrounding, and on top of the onions. Evenly distribute the butter among the onions, on the top center of each one. Uncovered, return the onions to oven and roast for another 30 minutes.
- Baste the onions with the juices from the bottom of the pan and turn the heat up to 350°F. Still uncovered, continue to roast for 1 to 2 more hours, basting them every 20 minutes with more juices from the bottom of the pan. (It's your call -- the longer you roast them, the more caramelized and soft they'll be.) And for an even deeper flavor, when you turn the oven up to 350°F, peel and cut the onions into quarters from the "X" at the top, before continuing to roast them.
- Cool and serve. Remove from the oven and let them cool in the pan. If you haven’t already done so, when they’re cool enough to touch, take off the skins and slice. Serve with the remaining fresh herbs.
Linger, Kristy Murray
Oh my goodness! There is nothing like the aroma coming from the kitchen of onions roasting in the oven. There are so many wonderful ways to use this recipe in meals. Also, I love the added tips you gave in this post. Thanks so much Valentina for sharing.
Valentina
Thank you, Kristy. Hope you love them! : -) ~Valentina
Liz
Oh, how I love onions! And roasted with herbs is a fabulous way to cook them!
Valentina
Thanks, Liz. Enjoy! : -) ~Valentina
Suzanne
These look delicious. Do you think I could make them in a Crock-Pot instead of the oven with the same results?
Valentina
Hi Suzanne. Thanks for writing in. Believe it or not, I don't have or use a Crock Pot, so I can't say exactly how they would turn out. This might be a goo guide. Hope it helps and enjoy! 🙂 ~Valentina
Eha
You do think of different courses for the same horses, don't you 🙂 ! I have certainly baked onions together with other root vegetables many a time but do not remember making them the solo heroes ! The idea does attract . . . probably as a side . . . with any 'spares' put aside for an extra when filling my wraps! Usually, I use rosemary apart from my other herbs but am more than willing to try . . . here goes . . .
Eha
Forgot the well-earned stars!
Valentina
😀
Valentina
Hi, Eha. I think "solo heros" is my favorite turn of phrase I've eve heard for a food/ingredient. I might just have to steal it. 😉 I love it, and thank you so much and enjoy! : -) ~Valentina
Sherry MacKay
Yes roasted onions are the best! How delicious!
Valentina
Thank you, Sherry. Enjoy! : -) ~Valentina
Dawn
Roasted veggies are the absolute best! I can only imagine how tender and sweet these onions are. Love your tip about using the dish afterwards to roast more veggies. Talk about adding tons of flavour!
Valentina
They are so sweet and delicious. Thank you, Dawn. Yes, reuse the caramelized pan, for sure! : -) ~Valentina
mimi rippee
How fabulous! A definitely unique side dish. It would be good with all kinds of mains!
Valentina
They are. Thank you, Mimi! : -) ~Valentina
David Scott Allen
While I cannot eat raw onions (just getting too old! Hahah!) and really don’t love the taste in my mouth (for days!), I absolutely ADORE cooked onions - such sweetness! I will definitely make these to go alongside my next roast chicken. What a match that will be.
Valentina
Thank you, David. Yes they become a whole different "animal" when cooked this way. 😉 Enjoy! ~Valentina
Jeff the Chef @ Make It Like a Man!
I love this! I'm a huge onion fan. I recenly saw a recipe like this, but when the onions were just about roasted, they smashed them and continued roasting, so they got a little bit crunchy.
Valentina
Hi, Jeff! Okay, now I'm definitely going to try that. Sounds amazing to add that second layer of texture. Thank you. : -) ~Valentina
Judee
I love making all kinds of vegetables but this is new to me. Looks delicious and I am going to have to give it a try. Visiting from Gluten Free A-Z Blog
Valentina
I hope you love it, Judee. Thank you! : -) ~Valentina
Marissa
These roasted onions look absolutely luscious, Valentina! I love it when secondary ingredients get a chance in the limelight and you can tell that these shine.
Valentina
Me too! Thank you, Marissa. : -) ~Valentina
2pots2cook
Beautiful! As Eha writes, I always roast onions with other vegetables but must change the habit! I wonder if these can be canned...
Valentina
Thanks so much, Davorka. I'm sure you could can them. The way you'd can jams and preserves. : -) ~Valentina
Velva- Evening With A Sandwich
Bravo to roasted onions! Roasted onions really bring out their natural sugars and caramels flavors-beautiful alone or served in another dish. Love this! Thanks you for the inspiration.
Best,
Velva
Valentina
Thank you so much for checking out my recipes! Hope you give this one a go. 🙂 ~Valentina