Place the pizza dough on the counter until it comes to cool room temperature, about 1 hour.
Make the mac and cheese
Spray a 10-inch (25-centimeter) round cake pan with nonstick cooking spray.
Boil 4 quarts (4 1/2 liters) water with 1 teaspoon (6 grams) salt. Add the macaroni and cook until al dente, 8 to 10 minutes. Drain the macaroni and then dump it in a large bowl.
Melt the butter in a medium saucepan over medium heat. Add the onion and sauté for 30 seconds. Add the flour, remaining 1 teaspoon (6 grams) salt, the dry mustard, paprika, and pepper and stir continuously until a paste forms. Add the milk and stir continuously until smooth. Simmer for about 5 minutes, until thickened. Stir 2 cups (227 grams) of the sharp Cheddar into the thickened sauce and keep stirring until it is smooth and melted.
Pour the cheese sauce over the macaroni and stir until it is all well combined. Scrape half the mac and cheese into the prepared pan. Sprinkle with the remaining 2 cups (227 grams) sharp Cheddar. Pour the rest of the mac and cheese on top and pat it down to form a cake. Chill for 1 hour.
Move an oven rack to the lowest position. Preheat the oven to 500°F (260°C) for 30 minutes.
Shape the dough into a round just slightly larger than your cake pan. Sprinkle with the mozzarella, 1 cup Cheddar, and Romano. Use a metal spatula to loosen the mac and cheese cake from the pan. Turn the pan over and carefully transfer the mac and cheese cake to a plate. Slide the mac and cheese onto the middle of the pizza, and top with the crushed crackers.
Bake the pizza for 13 to 15 minutes, until the crust is deep brown and the mac and cheese is bubbling. Check underneath with a metal spatula to ensure the bottom crust is deep brown too. Let the pizza rest for 5 minutes. Sprinkle with the chives, then cut the pizza into 8 wedges and serve.
This baked mac and cheese pizza recipe wasn't how I have experienced baked mac and cheese or cheese pizza in the past, but it was a very good hybrid, and I thoroughly enjoyed it. I see endless possibilities. I used a Jim Lahey recipe for the pizza dough and baked the pizza for 15 minutes.
Yum! Easy! Delicious! Simple! This baked mac and cheese pizza is the perfect lunch, dinner, school lunch, or dinner for the next day. Ideal combination of cheeses. And the Ritz crackers are a very nice touch on top.