These are actually cooked on the grill. It's been my experience that many people have never cooked hot cheese sandwiches this way. They are tasty, easy, and fast.
Sliced Cheese -- use a variety of cheeses to spice these up: pepper jack, colby, cheddar, etc.
Slippery Condiment* -- use butter, margarine, or mayonnaise. This must be the "full fat" version. Margarine or mayo that is "light" will not release from the grill easily.
*Flavor your spread if you'd like. Garlic, dill, or smoke flavoring stirred in it makes it even better!
Step 1: Prep
Get the grill going. Medium heat is perfectly sufficient for this.
Spread your butter/margarine/mayo on the outsides of your bread. I stack them in pairs with the spread on the inside until I'm ready to put it on the grill.