1. Crust: Preheat oven to 425 degrees with rack in center. Pulse cauliflower in a food processor until it resembles the texture of quinoa (you should have about 4 cups). In a large straight-sided skillet, blanch the cauliflower in salted boiling water until just tender, 2 to 3 minutes. Drain well and transfer to a clean dish towel. Cool slightly, then squeeze out as much moisture as possible. Transfer to a baking sheet lined with another towel to dry out further.

2. In a large bowl, stir together the cauliflower, cheeses, and egg. Season with salt and pepper. Work with hands until very well combined and mixture holds together. Transfer mixture to a parchment-lined rimmed baking sheet and press firmly into a 10-inch round about 1/4 inch thick. Bake until golden brown and firm, 25 to 30 minutes. Remove from oven and let cool slightly, 5 minutes.

3. Topping: Top crust with tomato sauce, mozzarella, and basil. Return to oven and bake until cheese has melted and toppings are golden, 10 to 12 minutes. Cool 10 minutes before slicing. Serve with additional basil and red-pepper flakes, if desired.