This isn’t an airy, light soufflé that floats off the table. This is a a savory, rich, cheesy dish with a bit of levity. The extra puff from the eggs saves it from being too decadent, and creates a delicious foundation for these classic flavors. If you don’t want to whip these together at the last minute, no worries. Just prep them the morning of, and hold them in the fridge, baking them for an extra minute or two.
3 tablespoons unsalted butter
1 sprig sage, leaves removed
6 tablespoons (3/4 stick) unsalted butter, plus more to butter a 6-cup gratin dish
6 tablespoons all-purpose flour
2 cups cold whole milk, room temp
1/2 teaspoon salt
1/2 teaspoon freshly ground black pepper
1 cup grated Swiss cheese, preferably Gruyere (about 3 ounces)
1 cup pureed roasted butternut squash
To roast the butternut squash, peel, deseed, and roughly chop the butternut squash. Coat in a few tablespoons of oil, season with salt and pepper, and roast at 425F for about 45 minutes, turning once. The squash should be tender and golden brown. Take out the squash, and add it to a blender to make puree. Set aside.
Preheat the oven to 400 degrees F.
First make the brown butter by melting the 3 tablespoons of unsalted butter over medium heat, add the sage leaves, and continue to cook the butter until the milk solids turn golden brown. Immediately pour the browned butter into a bowl, along with the sage, scraping the bottom of the pan to get all of the bits.
In a medium sized pot over medium heat, melt the 6 tablespoons of butter and add the flour, stirring and cooking for about a minute, until it smells nutty. Add about 2 tablespoons of milk at a time, whisking to combine. At first it’ll be super thick, but just keep adding liquid and stirring. You should end up with a thick, velvety sauce. If a little thin, cook and stir it for a few minutes until it reduces, or if too thick, add a little more milk. Take the sauce off the heat and season with salt and pepper. Taste and adjust if needed.
Add the eggs, the cheese, the butternut squash, and half the brown butter and sage to the white sauce, and mix well to combine. Pour into the buttered dish and bake for 35 to 40 minutes, or until the soufflé is puffy and well browned on top. For individual ones (about 8 ounces), bake for about 20 minutes. Drizzle with remaining brown butter and sage and serve immediately.