So this is a cooperative counting game!
You add an ingredient to the pizza, the next person either says "I'd eat that" (agreeing to the new topping plus all previous ingredients) and adds 1, then suggests their own new topping. Or they say no and the game resets.
A pizza base is the first thing and moves the count from 0 to 1 to start the game.
OK, I'll start:
Pizza base.
1
How about tomato paste?