recipes:broccoli_and_cauliflower_gratin [alephnull.com]

Ingredients

• 4 tbsp. (1/2 stick) unsalted butter, plus more for pan
• 1 medium head cauliflower (about 2 pounds), cored and sliced 1/4-inch thick
• 1 large head broccoli (about 1 1/2 pounds), trimmed and sliced 1/4-inch thick
• 6 tbsp. all-purpose flour
• 3 c. whole milk
• 1/4 tsp. freshly grated nutmeg
• 8 oz. Gruyère, grated (about 2 cups)
• Kosher salt and freshly ground black pepper