This is based on a recipe from George Foreman's book, Indoor Grilling Made Easy. His intro says, "These are more like hamburger panini, so the burgers are meant to be on the thinner side." I made mine on the George Foreman grill (somehow I've managed to collect about 3 of them in various sizes!); however, any panini maker would work, too. You can also adapt these for a flat griddle, preferably a grooved one, keeping in mind that where the instructions say "grill" you'll need to grill both sides of the patties and the sandwiches, adjusting cooking times accordingly.