Pizza With Onion and Provolone

Ingredients

• 5 tsp. kosher salt, plus more
• 6½ cups bread flour
• ¾ cup spelt or whole wheat flour
• 1 ¼-oz. envelope active dry yeast (about 2¼ tsp.)
• 3 Tbsp. extra-virgin olive oil, plus more
• All-purpose flour (for dusting)
• 10 oz. aged provolone cheese, thinly sliced
• 2 large onions, diced into ½" pieces
• 10 oz. low-moisture mozzarella, grated
• Flaky sea salt
• Freshly ground black pepper

Steps

1. Combine 5 tsp. kosher salt and 3 Tbsp. water in a small bowl and stir to dissolve salt; set aside.
2. Whisk bread and spelt flours and yeast in a large bowl to combine. Add 3 Tbsp. oil and 3 cups room-temperature water; mix with a rubber spatula until a large shaggy mass forms. Knead in bowl until dough forms a rough ball, about 4 minutes. Let rest, uncovered, 10 minutes.
3. Add reserved salt water to dough and knead until water is incorporated (dough will be very wet and shaggy), 5–10 minutes. Generously oil a bowl that is at least twice as big as dough and place dough in bowl; cover with plastic wrap. Let rest at room temperature 30 minutes.
4. Transfer dough to a clean work surface and fold in half over itself 3 times, turning 90° after each fold. Return to oiled bowl, arranging seam side down. Cover tightly with plastic wrap and chill dough overnight (it should double in size).
5. Place dough on a lightly floured surface and divide in half. Lightly flour tops of dough. Working with 1 piece at a time, fold each corner into center of dough. Rotate 90° and repeat process until you have a neat ball. Turn dough, seam side down. Generously flour two 18×13" rimmed baking sheets and place a ball on each baking sheet. Cover each with a damp kitchen towel. Set in a warm spot; let rise until dough is very relaxed, supple, and doubled in size, 2–3 hours.
6. Place racks in upper and lower thirds of oven; preheat to 500°. Transfer dough balls to a work surface and lightly oil baking sheets. Lightly flour work surface and set 1 ball of dough on top, seam side up. Release some air by pressing down into dough with your fingers. Stretch dough; continue working with your fingers until it is about the same size as baking sheets. Transfer to a baking sheet and stretch to fit, pressing into corners. Repeat with remaining ball of dough.
7. Scatter provolone over dough. Top with onions, then mozzarella. Drizzle with oil; season with kosher salt. Bake pizzas, rotating top to bottom and front to back halfway through, until crust is golden brown and onions are charred in spots, 12–15 minutes.
8. To serve, drizzle pizzas with more oil and season with sea salt and pepper; cut into squares.