Preheat the oven to 500°F (if using a baking sheet) or as high as it will go (if using a baking stone/steel; place the stone in the top third or place the steel in the bottom third of the oven before you start preheating). Let the oven preheat for at least 30 minutes. Then, if you’re using a baking stone or steel, switch the oven to Broil on high.
Place a skillet over medium-high heat and add the ground beef and sausage. Cook, breaking up the meat with a wooden spatula, just until it’s no longer pink, about 5 minutes. Scrape the cooked meat onto a plate, leaving the grease in the skillet. Return the pan to medium-high heat and add the chopped bacon. Cook, stirring, just until the pieces begin to brown around the edges, 3 to 5 minutes. Turn off the heat, transfer the bacon to the plate with the ground meat, and pour the grease from the skillet into a small heatproof ramekin. Blot the meat with a paper towel if it looks too greasy for your taste.
Stretch or roll out your dough to a 12- to 14-inch circle, then transfer it to a baking sheet / pizza pan or a lightly floured pizza peel (if using a baking stone/steel).
Prick the dough all over with a fork and brush the edges with some of the grease from cooking the meat. Add the sauce and spread it evenly, leaving a ½-inch border all around, then arrange the thinly sliced shallot or onion on top of the sauce, followed by half of the mozzarella cheese. Add the cooked meats, bacon, ham, and pepperoni, a pinch or two of pepper flakes (if desired), the remaining mozzarella, and the parmesan.
Transfer the pizza to the oven and bake until the crust is evenly browned on the bottom and the cheese has browned in spots—8 to 10 minutes on the baking sheet, 5 to 8 minutes on the baking stone/steel.
Take the pizza out of the oven and let it sit for a minute or two, then top with the chopped parsley and/or chives; slice and serve.