Melt butter in a heavy, large skillet or Dutch oven over medium-high heat. Add onions; cook for 10 minutes, stirring frequently. Reduce heat to medium-low. Cook for 20-25 minutes longer or until onions are golden brown, stirring occasionally. Remove onions from the skillet; cool completely.
Brown sausage in the same pan over medium heat; drain. Set aside.
Roll out and stretch pizza dough on a lightly floured surface to a 12-inch circle. Press dough onto the bottom and about 1 inch up sides of a greased 10-inch springform pan. Spread pizza sauce on dough bottom. Sprinkle with fontina.
Top with the onions, reserved sausage, red peppers, mozzarella and parmesan. Bake for 25-30 minutes or until crust is golden brown and cheese is bubbly. Cool slightly before serving.