sturdy bread (Village Bakery Walnut Bread is good)
American cheese (for texture)
gruyere (for flavor)
sautéed onions (see note)
washed baby spinach (remove tough stems)
mustard (to taste)
olive oil (use the good local stuff)
Note: sautéed onions keep in the fridge, so go ahead and make a panfull.
Slice onions as thinly as you can manage and toss in a heavy pan over medium heat with just a bit of oil. Cook, stirring when you think of it, until limp and starting to brown. Remove from pan. In the same pan that you cooked the onion in, layer cheeses, onions and spinach between two slices of bread. Add a little more oil if needed and grill, turning once or twice, until cheese is melted. Add mustard to taste.