SAUCE. Make the sauce up to 24 hours in advance. Reheat over low heat, stirring frequently. CAULIFLOWER. Use frozen cauliflower and defrost in the microwave. MAKE AHEAD. Make the casserole in the morning, then reheat in a 350°F oven for 15 minutes.
Prep Time 10 mins
Cook Time 50 mins
2 medium heads cauliflower, divided into florets, about 12 cups 4 tbsp butter 1 medium yellow or sweet onion, diced 2 cloves garlic, minced 4 tbsp all purpose flour 2 c whole milk 1 tsp kosher salt ½ tsp ground pepper ¼ tsp nutmeg 1 cup shredded cheddar cheese 1 cup shredded gruyere cheese ½ c panko breadcrumbs 1 tbsp melted butter
SAUTE. Heat butter in sauce pot over medium high heat until it melts, then foams. Add the onion and cook until softened, then add the garlic and cook until fragrant.
THICKEN. Sprinkle flour over the onions and garlic. Work it in with a rubber spatula until thickened and paste-like (this is called a roux).
ADD MILK. Gradually pour in the milk, whisking constantly to avoid clumping (it is now a bechamel sauce).
SIMMER. Simmer until the bechamel is thick and easily coats and clings to your spatula.
CHEESE PLEASE! Season with salt, pepper and nutmeg, then the add cheese in small batches.
WHISK WELL! Whisk after each addition until very smooth.
STEAM. Steam the cauliflower using your favorite method (stovetop, microwave, or instant pot).
TRANSFER. Transfer the steamed cauliflower to the casserole dish and arrange in a single layer.
SAUCE IT. Pour the cheesy sauce over the florets, then gently combine.
MAKE TOPPING. Combine the melted butter and breadcrumbs in a small dish until evenly moistened.
TOP IT. Sprinkle the buttery breadcrumbs over the casserole.
BAKE. Bake uncovered for 25-30 minutes, until bubbling and golden brown.
SERVE. Garnish with parsley and freshly grated nutmeg (if available); serve hot or warm.