Talk about vegetarian comfort food! Oh my! And you know what’s amazing about this? It’s full of potatoes and delicious creaminess, but it isn’t too rich or one bit heavy. It is however, delicious, packed with flavor, and satisfying!
I love the layering process involved in creating this incredible gratin. It definitely feels like I’m creating art when I make this — both in flavor and in design. If you ask me, there couldn’t be a better weekend cooking project! (Well, maybe you could also make a super yummy soup to go with the potatoes — I’m just sayin.’)
I’ve laid out the steps for assembly very carefully for you because I think the success of this dish is all in the slicing and the layering. The potatoes become almost like thin, flat pasta, and the Gruyère links it all together. I even love how the knife feels as it cuts into the finished gratin, gently working its way through each potato slice. It’s almost a hint as to how divine a texture you’ve created.
This is one of my favorite weekend recipes!
Potato Spinach Gratin Recipe
- About 5-1/4-pounds Idaho Russet potatoes
- 1 large brown onion
- 1 tablespoon finely minced garlic
- 5 cups half and half
- 1-1/2 teaspoons dried thyme
- 1/8 teaspoon nutmeg
- 1/4 teaspoon allspice
- 1 1/2 teaspoons sea salt
- 1/2 teaspoon white pepper
- 6 cups loosely packed spinach leaves
- 2-1/2 cups grated Gruyère cheese
- 1-1/2 tablespoons melted unsalted butter
- Fill a medium-sized mixing bowl with slightly salty ice water. Peel the onion and slice it very thinly (about 1/8-inch or less) on a mandoline slicer. Add the onion slices to this and let them soak for about 20 minutes. (This removes some of the sharpness, mellowing the flavor a bit.) Drain the onions very well and set them aside.
- In a large sauce pot, combine the half and half with the garlic, thyme, nutmeg and allspice. Bring to a boil and then immediately reduce to a low simmer. Simmer until the half and half has reduced by 1/4, about 20 to 30 minutes.
- Remove the pot from the stove, add the salt and white pepper, and let it cool to room temperature.
- Peel the potatoes and use the mandoline slicer to cut the them lengthwise, as thinly as possible, adding them to the half and half mixture as you go. (You're making lovely, long oval shapes here.) Make sure the slices aren't stuck together and that all of them become well coated with the mixture.
- Preheat the oven to 375 degrees F.
- To assemble the gratin:
- Use a pastry brush and a bit of the melted butter to coat the bottom and sides of an approximately 9 X 13 X 2-inch baking dish.
- Without wiping them off, one by one, pull the potato slices from the half and half mixture, layering them on the bottom of the baking pan -- you will do two layers at a time, the first layer should be vertical, and the second layer should be layered horizontally. Each slice should overlap the previous slice by about 1/2-inch or so.
- Sprinkle the potatoes lightly with salt and white pepper.
- Squeeze any remaining liquid out of the onions and place about 1/3 of them in a thin layer on top of the two layers of potatoes.
- Sprinkle about 3/4 cup of the Gruyère cheese. Add half of the spinach leaves, making sure to cover all of the onion and potato. (The spinach will not lay flat, and that's okay.)
- Repeat steps 1 to 5.
- Add another two layers of the potatoes and set aside the remaining 1/3 of the onions, 1 cup of cheese, and all of the half and half mixture.
- Cover the pan with plastic wrap and then put a second pan directly on top of the it -- ideally it's exactly the same size so that the bottom of the top pan is pressing directly onto the plastic-covered, top layer of potatoes.
- Now weigh down the top pan with weights -- canned food is perfect. Fill the top pan with as many cans as will fit.
- Place this entire set-up in the refrigerator for about 30 minutes. (This is how we drain any excess moisture.)
- Remove from the pans from refrigerator and the weights from the top pan. Very carefully and over the sink, pour out any excess liquid from one of the corners of the pan. Keep it covered with the plastic and hold the palm of one hand of the top surface of the gratin to be sure nothing slides during this process.
- Set the pan down, remove the plastic wrap completely and sprinkle the top with a bit more salt and white pepper. Then add the remaining onions and cheese.
- Stir the half and half mixture to ensure the garlic and herbs are not sitting at the bottom. Pour this mixture into the gratin until it goes about 3/4 the way up the sides of the pan. You will need to use your fingers to move the potatoes a tiny bit along the edges of the pan to let the half and half seep through. It's important to do this to be sure it's actually getting all the way to the bottom.
- Drizzle the top with the remaining melted butter, place the pan on a baking sheet and then place it in the preheated oven for about 50 minutes.
- Cover with foil and continue to bake for another 25 minutes.
- If the top of the gratin hasn't become golden brown, place it under the broiler briefly -- maybe 30 seconds. Let it sit for at least 20 minutes before cutting.
Recipe NotesYes, you can make this if you don't have a mandoline slicer! It will take more time, but you can use a Chef's knife to slice the onion and potatoes. Just cut them as absolutely thinly as possible!
Up to 1 day and at least 1 hour, 45 minutes ahead of time: slice, soak, and drain the onion.
At least 1 hour, 45 minutes ahead of time: Make the half and half mixture, slice the potatoes and assemble the gratin.
This is a dish that only gets better with time. You can make the entire thing up to 3 days ahead of time and reheat it, covered, in a 375 degree oven for about 30 minutes.