To begin, dice the onion. Melt the butter in a large pot or Dutch oven. Throw in the onion and cook until translucent.
Now dump in the diced tomatoes and stir to combine. Add the tomato juice.
Grill masters all over the world have noticed that when you grill a piece of meat and then anoint it with some kind of fat, it mixes with the meat juices and creates instant sauce