In a large skillet over medium-low heat add the butter to the pan and melt. Add the onions, bell pepper, and garlic. Cook until softened, stirring occasionally, 5 minutes. Transfer to a plate and set aside.
Return the skillet to the stove over medium-high heat, add the ground beef and brown the meat, breaking it up.
Cook until the meat is done, drain off any excess water or fat. Add the peppers and onions back to the pan with the meat.
Add the tomato sauce, ketchup, brown sugar, Worcestershire sauce, salt, and pepper. Stir to combine, bring to a simmer and reduce heat to low. Stirring occasionally, simmer for about 5-8 minutes until thickened but still saucy. Taste and adjust seasoning if necessary. Serve on top of buns of your choice.