Slide the pizza onto the stone and bake for about 4 minutes, until lightly golden and bubbling. Carefully sprinkle one-third of the pistachios over the pizza and bake for 2 minutes longer, until the crust is browned and the onions are very soft. Slide the pizza onto a work surface. Drizzle with olive oil, cut into wedges and serve. Repeat with the remaining dough and toppings.