In a large saute pan, melt butter over medium heat. Saute onions in butter until the onions are soft and dark brown, approximately 25 minutes. Stir in sugar, and continue cooking for 1 or 2 more minutes.
Preheat oven to 425 degrees F (220 degrees C).
Grease a pizza pan or cookie sheet, and press out the dough to desired thickness. Spread onions evenly over the dough, and top with crumbled Gorgonzola.