**Broccoli and Cauliflower Gratin**


**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

**Instructions**
  - Preheat oven to 375°F. Butter a shallow 3-quart baking dish. Arrange cauliflower and broccoli in the prepared dish.
  - Melt butter in a medium saucepan over medium heat. Add flour and cook, stirring, 2 minutes (do not let it darken). Slowly whisk in milk. 
  - Simmer, whisking occasionally, until slightly thickened, 3 to 4 minutes. Remove from heat and stir in nutmeg and 1 1/4 cups cheese. Season with salt and pepper. Pour over vegetables. Sprinkle with remaining 3/4 cup cheese.
  - Cover loosely with aluminum foil and bake for 15 minutes. Remove foil; bake until vegetables are tender and the top is golden brown, 20 to 25 minutes. Let stand 10 minutes before serving.