Cauliflower Mac and Cheese

Preheat the oven to 400 degrees. Position rack in middle of oven. Butter a 9 x 13 baking dish. Set aside.
Place cauliflower in microwave safe bowl(s), add 1/4 cup water, cover tightly with plastic wrap and microwave on high for 7 minutes, until cauliflower is just starting to soften. Remove from microwave, allow to cool slightly and drain. Set aside.
In a large dutch oven, melt 1/2 cup butter over medium-high heat. Add garlic and thyme, cook for 1 minute or until garlic is fragrant.
Add the flour and cook until lightly browned, about 1 - 2 minutes.
Whisk in milk, salt, mustard, hot sauce, black pepper, and nutmeg. Stir constantly until thickened, about 5 minutes.
Remove from heat and stir in the cheeses until melted.
Fold the cauliflower into the cheese mixture until coated.
Transfer cauliflower to prepared baking dish.
In a small bowl, combine the bread crumbs and melted butter until bread crumbs are moistened. Sprinkle bread crumb mixture over cauliflower. Place baking dish on a sheet pan and place on middle rack of oven.
Bake until edges are bubbling, 20 - 25 minutes. Serve hot!