If you have a bit of leftover white sauce, try spreading it on a piece of sandwich bread, fairly thickly. Top that with a thin slice of ham, then a slice of good quality cheese. If your oven has a toasting feature (or in a toaster oven), toast your open-faced sandwich for about 3 minutes. This got the bread nicely toasted on the bottom and the cheese was melted on the top. But I wanted a bit more on the top--I wanted the cheese to be golden, like a pizza. So I just switched to the broiler for about a minute.
Mmm, comfort food.
