The quesadilla is a regional favorite in the southwestern United States. It could be called a Mexican grilled cheese sandwich. It is made by putting filling ingredients on one flour tortilla, then setting a second flour tortilla on top. Filling vary dramatically, but the basic ingredient is cheese. They are easy to make if you own a quesadilla maker as the quesadilla bakes on both sides at the same time and does not need to be flipped. Tostadas and chalupas are open-faced "sandwiches."