Preheat oven to 425°F.
Prepare the Cauliflower. Add cauliflower florets to a 13 by 9-inch baking dish along with 2 tablespoons of oil, ½ teaspoon salt, and ¼ teaspoon black pepper. Toss to combine and spread cauliflower out in the dish. Bake in preheated oven for 15-20 minutes.
1 large head cauliflower, 2 Tbsp. oil, 1 tsp. salt, ¼ tsp. black pepper
Make the Sauce. While cauliflower is baking, add 2 tablespoons of butter and crushed garlic to a large skillet or saucepan. Sauté over medium heat for 1 minute. Sprinkle flour into the pan and whisk for 1-2 minutes, or until it begins to form a paste. Reduce heat to medium-low. Pour in room-temperature milk, ¼ cup at a time, whisking well after each addition. Wait to add the next amount until the sauce has thickened.
2 Tbsp. butter, 2 cloves garlic, 2 Tbsp. flour, 1 ½ cups milk
Add Cheese and Cauliflower. Once all of the milk is added, turn off the heat and mix in gruyere cheese, ¼ cup Parmesan cheese, ½ teaspoon salt, thyme, and coriander. Pour sauce over baked cauliflower and toss to combine.
1 tsp. salt, ¾ cup cheese, ½ cup Parmesan cheese, ¼ tsp. dried thyme, ¼ tsp. coriander
Top and Bake. Mix together remaining Parmesan cheese and breadcrumbs in a small bowl. Sprinkle over cauliflower. Reduce oven temperature to 400 °F and return cauliflower dish to oven for 20-25 minutes. For an extra crispy topping, broil casserole for 2-3 minutes under a high broil.
¼ cup Panko bread crumbs, ½ cup Parmesan cheese
Serve with cauliflower with fresh thyme and enjoy!