Special equipment: pizza stone, pizza peel
For the dough: Thoroughly blend the flour, salt and yeast in a medium bowl. Add 1 1/2 cups water and mix thoroughly with a wooden spoon or your hands.
Cover the bowl with plastic wrap or a kitchen towel and let rise at room temperature (about 72 degrees F) it has more than doubled, 18 hours. It will take longer in a chilly room and less time in a very warm one.
Place a pizza stone in the oven on the middle rack. Preheat the oven to 500 degrees F for 30 minutes. Switch to broil for 10 minutes, then back to 500 degrees F.
Flour a work surface and scrape out the dough. Divide it into 4 equal parts. For each portion, start with the right side of the dough and pull it toward the center; then do the same with the left, then the top, then the bottom. The order doesn't actually matter; what you want is four folds. Shape each portion into a round and turn seam-side down. Mold the dough into a neat circular mound. The mounds should not be sticky; if they are, dust with more flour.
If you don't intend to use the dough right away, wrap the balls individually in plastic and refrigerate for up to 3 days. Return to room temperature by leaving them out on the counter, covered in a damp cloth, for 2 to 3 hours before needed.
Place the dough on a floured pizza peel and spread into a 10- to 12-inch round. Sprinkle evenly with the garlic. Distribute the mozzarella, pecorino and Gruyere evenly over. Sprinkle with the pepper.
Slide the pie onto the stone with quick, jerking motions. Bake for 2 minutes.
Pull the rack partially out of the oven. Quickly add the spinach in what will look like a big mound (the spinach will reduce, the mound flattening, as spinach always does when it cooks). Sprinkle evenly with salt. Return the pie to the oven for 3 minutes 30 seconds to 4 minutes (somewhat longer with an electric oven), until the crust is charred in spots.
Using the peel, transfer the pizza to a tray or serving platter. Drizzle evenly with oil. Slice and serve immediately.
Don't freeze the dough, but you can store it in the refrigerator, wrapped in plastic, for up to 3 days. In effect, when you're set to use it, you have your own ready-made dough.
Recipe courtesy of Jim Lahey, Co. Restaurant and "My Pizza," Barnsley, England