In a large skillet over medium heat, melt the butter. Add the onion and sugar; reduce the heat to medium-low. Cook and stir for 20 to 25 minutes or until the onions are very tender and caramelized. Coarsely chop and set aside.
In a food processor combine the garbanzo beans, olive oil, sesame oil, garlic, rosemary, water, salt, and pepper. Process until smooth. Stir in 2 tablespoons of the shredded Asiago cheese. Transfer mixture to a 12- to 16-ounce individual casserole dish.
Top with the caramelized onions and remaining cheese. Bake for 8 to 10 minutes or until the cheese is browned and the hummus is heated through. Garnish with rosemary. Serve with baguette slices, pita chips, carrots or celery sticks.