In a large skillet over medium heat, melt 1 tablespoon of butter in the pan.
Place tortilla in the pan on top of the melted butter and sprinkle 1/2 cup of cheese on the entire tortilla.
Add 1/2 cup of the cooked and crumbled beef on top of one half of the cheese and spread 1 tablespoon of salsa on the other side.
Let the cheese melt for about 3-4 minutes and then fold the tortilla in half.
Let it cook for another minute and then flip it to ensure that the other side is getting browned to your liking and that the cheese is melted thoroughly.
Repeat with remaining tortillas and ingredients, adding more butter as needed.
Remove the quesadilla from the skillet and cut into wedges.
Serve with guacamole, sour cream, and additional salsa on the side.