Preheat oven to 200C/390F.Boil a large pot of water and add the cauliflower, cook for 5-8 minutes until the cauliflower is tender.Drain the cauliflower well and return to the warm pot.
Add the butter, salt and pepper.Blend with a stick blender until the cauliflower is a smooth puree.
Add the bacon grease along with half of the bacon into the cauliflower puree.Add half of the parmesan cheese into the cauliflower puree and mix well.Pour the cauliflower mixture into a casserole dish.Top with the remaining bacon, parmesan cheese and mozzarella cheese.Bake in the oven for 20 minutes, until the cheese is melted and browning.