Basil Pizza bursts with the wonderful, fresh flavor of basil — with both pesto and whole leaves throughout. *Whether you're using homemade dough, or pre-baked crusts, have them ready to go when you start.
Preheat the oven and stone/sheet pan. Preheat the oven to 500°F, with a pizza stone on center rack. If you don't have a pizza stone, place a sheet pan on the rack a few minutes before you assemble the pizzas.
Make the pesto. Add the basil, pine nuts, Parmesan and garlic to a food processor fitted with the blade attachment. Blend until the basil is in tiny pieces. Then add the tomato paste, lemon juice, olive oil and pinch of sugar, and blend until smooth. Season to taste with salt and pepper. (Here's How to Season to Taste.)
Prepare the pizza crust. Either shape your pizza dough into approximately 12-inch rounds, or set out your pre-baked approximately 12-inch rounds, on a lightly floured work surface.
Assemble the pizzas. Evenly divide the pesto among the two crusts, spreading it thinly. Then sprinkle each with equal amounts of the grated Mozzarella. Now divide the red onion slices between the two, and about half of the basil leaves.
Bake. Transfer the pizzas to the stone or baking sheet and drizzle about ½ tablespoon of the olive oil along the edges of the crusts. Place in the preheated 500°F oven, and bake until the crust is golden along the edges, about 15 minutes. (For pre-baked crusts, heat just long enough to melt the cheese and heat it through.)
Garnish, cut and serve. Once out of the oven, add the chili flakes (if desired), pine nuts, and the remaining fresh basil leaves. Then drizzle with the remaining olive oil, slice and serve.