Preheat your oven to 220°C (425°F).
Rinse the large cauliflower, remove the leaves, and chop it into smaller florets. Place them in a food processor and pulse until it resembles rice or fine crumbs.
Transfer the processed cauliflower to a microwave-safe bowl, cover it with a damp paper towel, and microwave for about 5-7 minutes until soft. Let it cool.
Once cooled, place the cauliflower in a clean kitchen towel and squeeze out as much moisture as possible. In a mixing bowl, combine the cauliflower with your choice of cheese (200g), one egg, and a pinch of salt. Mix until well combined.
Line a baking sheet with parchment paper. Transfer the cauliflower mixture to the sheet and shape it into a pizza crust, about 1/2 inch thick.
Bake the crust in the preheated oven for about 15-20 minutes, or until golden brown and crispy.
Remove the crust from the oven and spread the tomato sauce evenly over the base. Sprinkle the mozzarella cheese on top, followed by the sliced mushrooms.
Return the pizza to the oven and bake for an additional 10-15 minutes, or until the cheese is bubbly and melted.
Let the pizza cool for a few minutes, garnish with fresh basil leaves, slice, and serve warm!