1 1/2 lbs. lean ground beef
1 small onion, chopped fine
1/2 green bell pepper, chopped fine
salt and pepper to taste
4 tbsp. tomato paste, preferably no-salt
1 tsp. Worcestershire sauce
1 tsp. prepared yellow mustard
1 tbsp. cider vinegar
1 tbsp. brown sugar
1 c. water, more or less
6 hamburger buns
Relish or mustard, optional garnishes

Brown the beef in a large skillet over high heat. Drain off the excess fat. Reduce heat to medium-high. Add the onions, green peppers, salt and pepper. Sauté until the onions and peppers are softened, about 5 minutes. Add the tomato paste. Worcestershire sauce, mustard, vinegar, and brown sugar. Stir to combine. Add water until the sauce is the desired thickness. Reduce heat to medium-low; cover and simmer about 10 minutes so the flavors combine. Taste and adjust as needed. Serve on buns, garnished with relish, and or mustard if desired.