1. Place an oven rack on lowest position and preheat to 500°F.
2. On a lightly floured surface, roll dough into a 14-inch round. Generously sprinkle a baking sheet with cornmeal. Place dough on sheet.
3. Bake until dough feels dry, about 8 minutes.
4. Heat oil in a pan on medium-high. Whisk in 1 1/2 Tbsp. flour and pepper. Cook until bubbling, about 2 minutes. Whisk in milk, bring to a boil, reduce heat and simmer, whisking, until thickened, about 2 minutes. Stir in Parmesan and peas.
5. Spoon mixture on crust, leaving a 1/2-inch border. Bake until crust is crisp and topping is bubbling, about 5 minutes. Top with prosciutto. Cut into 8 slices. Serve.