Peel outer skins from garlic bulb, leaving cloves attached. Cut off top quarter of bulb. Place bulb, cut-side up, on a piece of aluminum foil. Drizzle with 1 tablespoon oil, and seal foil tightly over garlic.
Bake at 425° for 45 minutes or until soft. Remove from oven; cool. Scoop out garlic pulp, mash, and stir until smooth.
Preheat oven to 450° with a pizza stone on the bottom rack.
Blanch nettle leaves in salted boiling water 1 minute, drain, and plunge into ice water. Remove nettle leaves from water, wringing out excess, and set aside. (If using spinach, place in a microwave-safe bowl, and heat at high 3 minutes. Set aside.)
Sprinkle surface with semolina flour, and roll Pizza Dough into a 12-inch circle.
Spread dough with mashed garlic (garlic won't cover entire surface); sprinkle with crushed red pepper and black pepper. Sprinkle with Pecorino Romano and thyme.
Roughly chop nettles, and spread over thyme. Sprinkle mozzarella, provolone, and fontina evenly on pizza. Carefully slide pizza onto the preheated stone; bake 6 to 8 minutes or until edges are lightly browned and crispy. Slice, and drizzle with extra-virgin olive oil to taste.