Sloppy Joes

During a recent move, I had neglected to remember my spices; the food I've been cooking has taken on a somewhat rudimentary flavouring scheme. That is, everything I'm eating is flavoured with salt, pepper, and some combination of ketchup and mustard. Still, I have to admit that these satisfy all of my deepest comfort food needs.
Start by sauteeing

2 tbsp butter
1 medium onion, finely chopped

at a very low temperature until the onion is translucent and sweet, about 10 minutes. Then add

1 pound lean ground beef

and fry until the meat is cooked through. Then add

1/2 teaspoon garlic powder
1 teaspoon prepared yellow mustard
3/4 cup ketchup
3 teaspoons brown sugar
salt to taste
ground black pepper to taste

Serve the whole mess on a white but or as a sandwich between a couple of slices of white bread.