1Preheat an oven to 200 degrees f and arrange a baking sheet in the oven.
2In a large non-stick skillet over medium heat, warm the oil. add the bell peppers and cook, stirring occasionally, until lightly browned and tender, 8 min. transfer to a plate and set aside.
3Lightly spread butter on one side of each tortilla. Lay the tortillas, buttered side down on a work surface. Arrange ½ cup of cheese on half of each tortilla, leaving a 1-inch border at the edge. Arrange the bell pepper and beef on top, then fold the tortillas in half over the fillings.
4Carefully wipe out the skillet. Rewarm the skillet over medium high heat. Add 2 of the quesadillas and cook, covered, until golden light brown on the bottom, 3-4 minutes. Carefully turn and cook, uncovered, until golden brown on the other bottom half and the cheese has melted, 1-2 minutes. Transfer the finished quesadillas to the baking sheet in the oven. Carefully wipe out the skillet and repeat with the remaining quesadillas.
5Cut each quesadilla into 2 wedges. Serve with abundant molcajete salsa.
