In a medium saucepan over medium heat add the 3 tbsp. of butter. Let it melt and add the chopped onion. Sautee the onion in the butter. The chopped onions should appear soft and clear. Add your sugar and mix well in the sauce pan.
Add the drained cans of pork and beans to the butter, chopped onions, and sugar mixture. Stir well mixing all ingredients together over the medium heat. Add the ketchup next and stir well. Then at last add your bacon grease. I always save my bacon grease and use it in lots of dishes. So when I have it on hand it is good to use to flavor soup beans, green beans, baked beans, and corn bread.
Turn the heat down on low and let simmer 5 to 10 minutes. (You can use bar b que instead of ketchup if you are having a bar b que dinner) Serve hot as a side. This is not a healthy side but we all do like to eat what tastes good and not what is good for you. Come on. Admit it. Once you try these you will not fix them no other way. Enjoy!
Just double the recipe if you are cooking for a large group.