Preheat oven to 375 degrees F.
Grease a medium casserole dish with butter or oil. Bring a large pot of water to boil, seasoning the water with salt.
Boil the cauliflower until slightly tender, about 5-8 minutes. Drain well and return to the warm pan to steam off more water.
Mix bacon into the cauliflower and transfer the mixture to the baking dish, distributing evenly.
To make the sauce: On medium-low heat, simmer the heavy cream. Whisk in cream cheese until creamy. Add salt, pepper, garlic powder, 1/2 cup blue cheese, and 1 1/2 cup cheddar cheese. Mix until creamy.
Pour the sauce evenly over the cauliflower. Top the dish with the remaining blue cheese and cheddar cheese.
Bake for 10-12 minutes, then broil for 3-4 minutes to crisp and brown the top.
Allow to cool for 5-10 minutes and serve.