Heat 1 tablespoon oil in large nonstick skillet over medium-high heat. Add onions and sugar. Cook until dark brown and tender, stirring frequently, about 16 minutes. Mix in vinegar and crushed pepper. Cook until mixture is thick, about 1 to 2 minutes more. Season marmalade generously to taste with salt and pepper.
Meanwhile, preheat oven to 500°F. Roll pizza dough out onto the back of a baking sheet, sprinkled with cornmeal. Brush with remaining 1 tablespoon of oil; sprinkle with salt. Spread onion marmalade over the crust, dollop ricotta all over the onion layer and top with slices of prosciutto. Bake until caramelized and crusty, about 10 to 12 minutes.
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