Line a rimmed baking sheet with parchment paper, and preheat oven to 425ºF.
Place the cauliflower in a microwave safe bowl and add a splash of water. Cover. Microwave for 3 minutes or until tender. Allow to cool.
Place cauliflower in a high powered blender or food processor and pulse until fully chopped and in tiny pieces. It will almost be grated.
Add the egg, 1 1/4 cups mozzarella cheese, parmesan cheese, garlic salt, pepper, red pepper flakes, and basil. Stir to combine all of the ingredients.
Pour the cauliflower mixture onto the baking sheet and form the shape of crust you want. Pat down to create a flat surface.
Lightly spray with cooking spray, then bake for 15-20 minutes or until golden and firm to the touch.
Spoon on the sauce, followed by both types of cheeses, leeks, mushrooms, and pepperonis.
Bake for other 10 minutes until melty.