Swiss Chard & Sweet Potato Gratin

Heat your 4 cups of milk and place next to the stove. In a medium pot, heat the butter over medium heat until starting to foam. Add the 5 tablespoons all purpose flour, and cook, stirring constantly, until the butter and flour mixture (the roux) starts to get golden in color.

Add your warm milk to the pot while constantly stirring with your whisk. Turn the heat up to high and continue whisking until the liquid begins to boil (this could take a few minutes - it's important to keep whisking it this whole time).

Once the pot reaches a boil, lower the heat and simmer, stirring with a whisk every so often for ~20 minutes, until the sauce is nice and thickened. It should coat the back of a spoon and be the consistency of a smooth gravy.

Season the béchamel with 1/2 teaspoon of salt and fresh ground pepper. Turn off the heat, and stir in the 1/2 cup gruyere cheese. Taste and adjust seasoning as necessary. Set aside in the pot covered by a lid if using shortly to assemble the gratin. If making it in advance, refrigerate in an airtight container for up to 1 week.

Pre heat your oven to 400F. Separate all the chard leaves from the stems. Thinly slice the stems and place them in a mixing bowl. Stack a bunch of the chard leaves and roughly chop them. Repeat with the remaining leaves. Dice your onion and mince the 4 cloves of garlic.

Heat the 2 tablespoons unsalted butter and 2 tablespoons olive oil over medium heat in a large, wide pan or shallow pot. Once the butter is foaming, add the diced onion and 1/2 teaspoon kosher salt. Cook, stirring, until the onions are starting to soften. Add the sliced chard stems, another 1/2 teaspoon kosher salt, several grinds of pepper, and 1/8 teaspoon of ground nutmeg and sauté until the stems are softened (~5 minutes). When the chard stems are softened, add the minced garlic and stir to incorporate.

Once the stems are softened, start adding handfuls of the chopped chard leaves to the pot. Add as much as you can fit without it spilling over and stir into the softened stems. You can cover the pot with the lid to help them steam and cook down. Repeat with the remaining chopped chard leaves until they are all cooked down. Add a pinch more kosher salt and a few grinds of pepper. Turn off the heat and set aside.

While the chard is cooking, peel and slice your sweet potatoes, and chop your Italian parsley. Tear the thyme leaves off the stems and add them to the chopped parsley.

Assemble! Place ~1/4 cup of the béchamel into the bottom of a 9x13 baking dish. Using an offset spatula or the back of a spoon, spread it around the bottom of the dish. Cover the béchamel with an even layer of the sliced sweet potatoes, a pinch of kosher salt and pepper, followed by half of the cooked Swiss chard. Scatter half of the chopped parsley and thyme over the chard, followed by 1/3 cup of the grated gruyere.

Cover with another layer of béchamel and spread it evenly over the layer below. Repeat with another layer of sliced sweet potato, salt and pepper, the remaining chard, the remaining herbs, and another 1/3 cup of grated gruyere.

Spread a final layer of béchamel over the top of the assembled gratin (you may not need to use all the béchamel, but more is more for this dish!). Top it with the remaining 1/3 cup grated gruyere and the 1/3 cup grated parmesan cheese. You can prep the dish ahead through this step, wrap tightly in plastic wrap and refrigerate overnight.

When read to bake, make sure your oven is at 400F. Place the baking dish in the oven, uncovered, and bake for ~30-40 minutes until the top is golden and bubbling. Depending on the oven, the top can start to brown and look done before the sweet potato is cooked through inside - you can test this by cutting into it a little bit, it should cut very easily through if it's cooked. If you feel any resistance from the sweet potatoes, continue to bake 10 minutes more (and if the top is getting too brown, you can cover it with foil).

Remove from the oven and let cool for a few minutes, then serve!