Method

Preheat oven to 425°F (220°C).

In large skillet, heat butter with oil over high heat; cook onions, sugar and rosemary, stirring occasionally, for 5 minutes. Reduce heat to medium-high; cook, stirring and scraping bottom of pan often, for 10 to 15 minutes or until golden brown and very soft. Let cool to room temperature. (Recipe can be prepared to this point and refrigerated in airtight container for up to 24 hours.)

In small bowl, stir together cheese, salt and pepper; evenly arrange over half of each tortilla. Evenly divide onions over cheese. Fold uncovered half over filling; press edges together. (Quesadillas can be prepared to this point, covered and refrigerated for up to 3 hours.)

Place on baking sheet; bake in oven turning halfway through, for about 10 minutes or until browned and crisp. To serve, cut into wedges.