Caramelizing the onions takes a bit of time, but the flavor is well worth it in these tasty quesadillas. Enjoy with a Brennans Amber. 6 appetizer servings.
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. Cool to room temperature.
Preheat oven to 350F. Sprinkle cheese over half of each tortilla, dividing equally. Sprinkle prosciutto and sautéed onion over cheese. Season with pepper. Fold other half of each tortilla over cheese mixture. Brush tortilla with some melted butter.
Brush large heavy skillet with some melted butter. Place over medium-high heat. Working in batches, cook quesadillas just until brown spots appear, brushing with butter between batches, about 2 minutes per side. Transfer quesadillas to large heavy baking sheet. Bake until tortillas are golden and cheese melts, about 5 minutes. Transfer quesadillas to work surface. Cut each into 6 triangles. Arrange on platter and serve hot.