1. Preheat oven to 450°. (For a crispy crust, preheat a pizza stone on the lowest rack in the oven.)
2. Melt butter in a large skillet over medium heat. Add onions; sauté, stirring occasionally, 20 minutes or until soft and golden brown. Stir in vinegar, salt, and pepper.
3. Roll dough to 1/4-inch thickness on a floured baking sheet or pizza peel. Brush edges of crust with olive oil. Spread onion mixture to edges of crust; top with blue cheese, walnuts, and figs, if desired.
4. If desired, transfer pizza to pizza stone dusted with cornmeal or semolina flour; bake 10 to 12 minutes. Remove from oven, and sprinkle with arugula and prosciutto. Drizzle with additional olive oil, if desired.