Heat the oil in a large skillet over medium heat, then add the butter and allow to melt.
Add the ground beef and brown in the skillet, breaking it up as it browns.
Remove the ground beef to a plate, but leave as much of the oil/butter in the skillet as you can.
In the same skillet, sauté the onions and pepper until soft.
Add the garlic and cook until fragrant.
Add the beef back to the skillet, then add the tomato paste and stir through and allow this to cook for a little while (this browns the tomato paste and deepens the flavor).
Add the tomato sauce, ketchup, Worcestershire sauce, Brown sugar and seasonings and stir through.
Cook over medium low for about 15 minutes, until it is as thick as you like.
Serve over toasted buns, and garnish with dill pickle slices.
You can make a large batch and freeze this for future meals.