This is my favorite and most easily made panini. I don't have a panini press so I just use my George Foreman grill. This is a just the basic recipe and is delicious as is, but if you want to give it some more pizzaz add some apple or pear slices.
Spray grill or panini press with non-stick cooking spray. (I prefer olive oil cooking spray because I think it tastes a lot better).
Spread mayonaise and mustard on bread to your preference.
Put prosciutto on bottom piece of bread, top with cheese and second piece of bread. (Putting the cheese on top allows it to melt into the rest of the sandwich rather than just out and onto the grill.).