Preheat the oven to 400°F (205°C) and line a sheet pan with parchment paper.
Pulse the cauliflower into rice-sized pieces, then steam for 8–10 minutes until tender.
Let the cauliflower cool slightly, then squeeze it in a clean towel until very dry (remove at least 1/2 cup liquid).
Mix dried cauliflower with egg, Parmesan, garlic, Italian seasoning, salt, and pepper until it holds together.
Press the mixture into a 10–11 inch circle about 1/4 inch thick on the parchment-lined pan.
Bake for 20–25 minutes until golden and firm, rotating the pan halfway through.
(Optional) Flip the crust carefully and bake 5 more minutes for extra crispness.
Add light toppings (keep sauce to 2–3 tbsp), then bake 5–8 minutes until warmed through.