Cheese (pre-sliced is easiest – not too thin, and nothing wet like mozzarella). I use Dutch edam but I’ve tried cheddar before too. You can also do little piles of shredded cheese but try to make the pile flat/even.
Bake for about ten minutes (start checking earlier) until the edges are bubbly and the centre is JUST lightly brown. Don’t let them get too brown or they go bitter.
Eat with tuna salad, guacamole, more cheese, whatever you want. You can also make big ones and bend them into taco shapes before they cool.