Heat your oven to 500°F (or as hot as it goes) with a rack in the center. Coat either 1 13×18-inch rimmed half-sheet pan or 2 12-inch round pizza pans lightly with olive oil. Sprinkle lightly with cornmeal. Use your fingers to stretch dough to the edges of the pan(s). If it puts up a lot of resistance, let it rest for 5 to 10 minutes, and resume working the dough to the sides. Top dough(s) with cheeses, a few grinds of black pepper, and garlic. Heap spinach all over; season with salt. Bake pizza until spinach is wilted and slightly browned, about 10 minutes. Remove pizza from oven and drizzle with olive oil. Cut and serve immediately.