Smoked Gouda and Caramelized Onion Quesadillas

2 tablespoons (1/4 stick) butter
1 onion, thinly sliced
1 tablespoon golden brown sugar
1/4 teaspoon white wine vinegar
smoked Gouda cheese, sliced thin
green apple, sliced thin
Melt 2 tablespoons butter in heavy medium skillet over medium heat. Add onion, brown sugar and vinegar; sauté until onion is golden brown, stirring frequently, about 25 minutes. Remove from heat.
Heat a heavy skillet and put in a bit of butter or spray a tortilla with Pam. Layer cheese, onions and apple slices and top with another tortilla. Brush top tortilla with melted butter or spray with Pam.
Cook quesadillas just until brown spots appear, flip and cook until golden. Cut into wedges and serve