Preheat oven to 220 C / Gas 7. Line a muffin tin with baking parchment squares.
Grate cauliflower into a microwave-safe bowl using a fine grater. Chop up any remaining pieces that are too small to grate.
Microwave cauliflower until soft and tender, 4 to 6 minutes. Pour cauliflower into a clean tea towel; cool until easily handled, 15 to 20 minutes.
Wrap the tea towel around the cauliflower and squeeze out as much liquid as possible; the drier the cauliflower is, the better it will hold together as a base once mixed with the other ingredients.
Combine cauliflower, 100g of the mozzarella cheese, Parmesan cheese, egg, salt, pepper, garlic powder and onion powder in a large bowl.
Scoop cauliflower base mixture into prepared muffin tin, dividing the mixture evenly among the holes. Pat down cauliflower mixture with the back of a spoon, making it compact.
Bake in the preheated oven until golden brown, about 15 minutes.
Spoon a small amount of pizza sauce onto each cauliflower base. Top with remaining mozzarella cheese.
Bake until golden brown and cheese is melted, about 15 minutes. Let sit in pan for 5 minutes before moving each bite to a cooling rack. Let cool for 10 minutes. Peel parchment paper squares off the bases and serve on a platter.
If you've got a food processor, cut the cauliflower into smaller chunks and process until fine.