Meatball Pizza

Ingredients

• 1 large slice stale white bread, crust removed
• 1/3 cup warm water
• 4 ounces ground veal or beef, very cold
• 3 ounces sweet or hot italian sausage, very cold, casing removed
• 1 small garlic clove, minced
• 1 tablespoons minced fresh flat-leaf parsley
• 1 large egg white, lightly beaten
• 2 ounces parmigiano-reggiano, finely grated
• salt and freshly ground black pepper
• 1 tablespoon olive oil, plus more for shaping and brushing
• 1 small yellow onion, diced
• salt
• 1 ball semolina pizza dough, at room temperature
• 3/4 cup simple pizza sauce
• 4 ounces whole-milk, low-moisture mozzarella cheese, shredded