Preheat oven to 425 degrees. If you're using raw pizza dough, precook it according to the package directions for 5 minutes. If you're using cooked dough, skip this step.
Heat 2 tablespoons of butter in a skillet. Add the sliced onion. Season with salt & pepper. Cook, on medium-high heat, for about 7-10 minutes or until the onions are lightly browned & caramelized. Stir in ¼ cup brown sugar. Cook on medium heat & cook for another 2 minutes. Remove from heat.
Now, over to the pizza crust. Drizzle on olive oil, sprinkle on a little salt, followed by a little Parmesan (grated or shredded).
Lay slices of mozzarella evenly over the top of the crust. Arrange caramelized onions over the top of the mozzarella. Lay slices of the prosciutto over the onions. Sprinkle on a little parmesan cheese.
Bake for 10-15 minutes in the oven, or until the bottom of the crust is golden brown, being careful not to cook for too long. If you're using a precooked crust, cook according to the package instructions. Remove from oven, let cool for 5 minutes, and cut into squares. Serve immediately.