Heat skillet on low heat with just a pat of butter. Lay a tortilla in the skillet and sprinkle cheese on top leaving about an inch of space around the edges. Warm the tortilla over low heat. The cheese will begin to melt a little. Lay another tortilla on top and continue to cook on low. Slightly lift up the edge of the bottom tortilla to make sure it is brown and then with a large flat spatula, flip it over, holding the top tortilla down with your fingers as you flip.
Allow the tortilla to brown for about two minutes, then using a spatula, gently lift the edge so you can check to make sure it has browned enough. When it is brown and cheese is all gooey, transfer to individual plates or a large platter. Repeat with remaining butter and tortillas. Top them with the sour cream, salsa and guacamole.