French Onion Mushroom Casserole Recipe

Imagine the best bowl of French Onion Soup you’ve ever had, only in casserole form.  The perfectly toasted French bread, the melting Swiss cheese, the caramelized onions, and all of the hearty, warm flavors of beef, garlic and mushrooms.French Onion Mushroom Casserole Recipe - It's like the best bowl of French Onion Soup you've ever had, only in the form of a casserole. It's the top of the soup -- the perfectly toasted French bread, the melting Swiss cheese, the caramelized onions, and all of the hearty, warm flavors of beef, garlic and mushrooms.Creative and comforting food for casual entertaining.  That’s what I do — here on my blog, and in my kitchen. I love cooking for others, but the “entertaining” part could be switched out for “eating,” if your prefer.  😉

The “creative and comforting” part is not only about the end result, but is so much about the cooking process.  While I always loved cooking, it wasn’t until I studied it in Culinary school, that the process became more important to me.French Onion Mushroom Casserole Recipe - It's like the best bowl of French Onion Soup you've ever had, only in the form of a casserole. It's the top of the soup -- the perfectly toasted French bread, the melting Swiss cheese, the caramelized onions, and all of the hearty, warm flavors of beef, garlic and mushrooms.Learning how and when to add certain ingredients to a pan, what to finish with and why — it all just fascinated me.

Patience is imperative.

You must not deglaze the pan until you’ve properly browned the ingredients.  French Onion Mushroom Casserole Recipe - It's like the best bowl of French Onion Soup you've ever had, only in the form of a casserole. It's the top of the soup -- the perfectly toasted French bread, the melting Swiss cheese, the caramelized onions, and all of the hearty, warm flavors of beef, garlic and mushrooms.You must wait several seconds after adding herbs, before moving on.  Let the aromatics come out into the room first.French Onion Mushroom Casserole Recipe - It's like the best bowl of French Onion Soup you've ever had, only in the form of a casserole. It's the top of the soup -- the perfectly toasted French bread, the melting Swiss cheese, the caramelized onions, and all of the hearty, warm flavors of beef, garlic and mushrooms.You must let a sauce thicken properly.  If you add a thickener, but don’t let it bubble, you will not see what consistency you’ve reached.  French Onion Mushroom Casserole Recipe - It's like the best bowl of French Onion Soup you've ever had, only in the form of a casserole. It's the top of the soup -- the perfectly toasted French bread, the melting Swiss cheese, the caramelized onions, and all of the hearty, warm flavors of beef, garlic and mushrooms.Layer ingredients carefully.  The order in which foods are layered can make a difference in how each bite feels in your mouth.  French Onion Mushroom Casserole Recipe - It's like the best bowl of French Onion Soup you've ever had, only in the form of a casserole. It's the top of the soup -- the perfectly toasted French bread, the melting Swiss cheese, the caramelized onions, and all of the hearty, warm flavors of beef, garlic and mushrooms.You must not pull things from the oven too quickly — it’s not about time, it about the aroma and the appearance. French Onion Mushroom Casserole Recipe - It's like the best bowl of French Onion Soup you've ever had, only in the form of a casserole. It's the top of the soup -- the perfectly toasted French bread, the melting Swiss cheese, the caramelized onions, and all of the hearty, warm flavors of beef, garlic and mushrooms.It’s been years since Culinary school, but I still find so much pleasure in the process.  Sure, a quick and easy dinner is essential on some nights, but when time allows, I could spend all day in the process.

The entire process begins with an idea, of course.  In this case, the idea was born when Melissa’s Produce delivered a huge bundle of gorgeous multi-colored pearl onions to my door.  What was I to do?  Make them the star of a dish, obviously.French Onion Mushroom Casserole Recipe - It's like the best bowl of French Onion Soup you've ever had, only in the form of a casserole. It's the top of the soup -- the perfectly toasted French bread, the melting Swiss cheese, the caramelized onions, and all of the hearty, warm flavors of beef, garlic and mushrooms.This is not a sponsored post.  Melissa’s sent me the pearl onions for recipe testing.  As always, all opinions are my own and I only write about things I truly love.

4.7 from 3 reviews
French Onion Mushroom Casserole Recipe
 
Prep time
Total time
 
Peeling pearl onions can be very easy if you follow this step-by-step photographic guide.
Serves: 6 to 8
Ingredients
  • Olive oil for the pan
  • 1¾-pounds pearl onions, peeled (here's How to Easily Peel Pearl Onions)
  • 8-ounces washed and dried Crimini mushrooms, thinly sliced
  • 1½ tablespoons finely chopped, fresh thyme
  • 2 cups beef broth
  • ½ cup dry red wine
  • 5 tablespoons unsalted, softened butter, divided
  • 2 tablespoons all-purpose flour
  • 1 (approximately 2-foot) thin French baguette
  • 1½ tablespoons minced garlic, divided
  • 1½ cups grated Swiss cheese, divided
  • sea salt and freshly ground black pepper
Instructions
  1. Preheat the oven to 375 degrees F, and adjust a rack to the top third.
  2. Once you've peeled the onions (here's how) -- coat the bottom of a large sauté pan with olive oil and place it over medium heat.
  3. Add the peeled onions and sauté them, stirring periodically, until they're nicely caramelized, 15 to 20 minutes.
  4. Add a bit more oil to the pan, and add the mushrooms. Again, stirring periodically, sauté until they're nicely caramelized, about 10 minutes. Mix in the thyme and cook until it's very aromatic, about 30 seconds.
  5. Turn he heat to low and pour in the beef broth and wine to deglaze the pan. Use a wooden spatula (if you have one -- otherwise a spoon), to gently scrape any bits of stuck onion and/or mushroom from the bottom of the pan, and incorporate it into the liquid. Turn the heat to high and bring to a boil. Then reduce the heat to low again and simmer.
  6. Meanwhile, add 2 tablespoons of the butter to a small sauté pan and melt it. With the heat on low, whisk in the flour. (This is a roux and will thicken the sauce.)
  7. Using a whisk, mix the roux into the onions. Again, turn the heat to high and bring to a boil. Then immediately reduce the heat to the lowest setting and let this simmer, uncovered, for about 15 minutes. Season to taste with salt and pepper. (Here's How to Season to Taste.)
  8. While the sauce is simmering, cut about about ¾ of the baguette into thin slices, diagonally -- about ½-inch thick. Place the slices on a baking sheet and set aside.
  9. In a small bowl, mix 2 tablespoons of the butter with 1 tablespoon of the garlic and spread each slice of bread with it. Sprinkle with salt and pepper and place the baking sheet in the preheated 375 degree F oven until the edges are golden, 10 to 15 minutes. Remove from the oven and add the now toasted slices to the bottom of an (approximately) 9 x 13 x 2-inch baking dish. Set aside, and leave the oven on.
  10. Cut the remaining ¼ of the baguette into small cubes and add them to the same baking sheet you used for the slices. Mix the remaining 1 tablespoon of butter with the remaining ½ tablespoon of garlic and melt it in the microwave, or a tiny sauté pan. Drizzle this over the cubed bread on the baking sheet and sprinkle with salt and pepper. Toss gently with your hands to be sure it's well mixed. (Be careful as the baking sheet might still be hot!) Place this in the oven (still at 375 degrees F), until golden, 10 to 15 minutes. Remove from the oven and set aside. Leave the oven on.
  11. Sprinkle ½ cup of the cheese evenly over the toasted slices of bread in the baking dish.
  12. Pour the onion sauce evenly on top and then evenly distribute the cubed, toasted bread on top of that.
  13. Sprinkle evenly with the remaining 1 cup of cheese.
  14. Bake in the (still) preheated 375 degree F oven until it's bubbling along the edges, about 20 minutes.
  15. Let it cool for about 10 minutes and then serve.

 

Share on YummlyPin on PinterestShare on StumbleUponShare on FacebookTweet about this on TwitterShare on Google+Share on LinkedInShare on TumblrEmail this to someonePrint this page

Subscribe to Cooking On The Weekends so you don’t miss any new, mouth-watering recipes!

Comments

    • valentina says

      Perfect idea, Helen — and you could totally mix it up and use potatoes instead of the bread for a gluten-free version. 🙂

  1. linda says

    The more I cook the more I rely how the ingredients look and smell while cooking to know when a dish comes together. I suppose you could put something on a plate in 10 minutes or you can cook a really good meal.

  2. Julie says

    I made this for a pot luck I went to yesterday – it was quite the labor or love – was absolutely delicious!!! Although next time I would rather cut the labor and use frozen pearl onions – has anyone made this dish with them?

    • valentina says

      Hi Julie, you could absolutely use frozen peeled onions — just make sure they are well thawed and drained of any excess moisture before you begin. So happy it was a hit! Thanks for sharing. 🙂

  3. Jenna says

    Hi! I want to make this for easter tomorrow! I am worried that it will get soggy tho if made ahead of time… does it keep well for a bit of time?

    • valentina says

      Yes, Jenna — you can definitely make this ahead of time! You can get it all assembled tonight and put it in the oven tomorrow. OR, you can bake it tonight, letting it cool completely and then refrigerate. Take it out of the refrigerator in the morning, at least 30 minutes before serving, and place it in the oven again (375 degrees F) to heat it through, about 15 to 20 minutes. Serve! Enjoy!

Leave a Reply

Your email address will not be published. Required fields are marked *

Rate this recipe: