Remove upper grill plate to expose broiler.
Attach lower griddle plate. Preheat Grill & Broil on LOW Broil.
In medium saucepan, melt butter over medium-high heat. Add onions, sugar and ¼ tsp. salt and cook for about 5 minutes. Turn down heat to medium-low and continue to cook until onions caramelize, about 10-15 minutes.
Meanwhile, in medium bowl, mix cream cheese with 1 Tbsp. Fontina, ½ cup Parmesan, ¼ tsp. salt, pepper, parsley and garlic powder.
Once onions are caramelized, remove from heat and fold into cream cheese mixture.
Spread mixture into preheated griddle plate and cook on LOW Broil for 3 minutes.
Add remaining Fontina and Parmesan on top and cook on HIGH Broil for 3 additional minutes until cheese browns.
Serve hot with toasted baguette slices.