Yet another winner from The Cookbook Junkie. This is the sloppy joe (or, if you're from where I'm from, Beef BBQ) of my childhood memories. Good on squishy rolls, but I like to eat it open-face on a piece of bread with chopped fresh tomatoes. Mmmmm!
1 lb ground beef
Chopped onion to taste
1 tsp mustard
½ C ketchup
1 T vinegar
1 - 2 T sugar
Salt and pepper to taste
Brown hamburger and onion in frying pan. Combine remaining ingredients and pour over meat. Simmer for 10 minutes.