Best Ever Grilled Cheese Sandwich

1. Melt the butter in a hot skillet and saute the onion until translucent and well-cooked.
2. Put the bread, butter side down, on a hot skillet. Put the slice of cheese, tomato, and onion on top. Place the other piece of bread, butter side up, on top. Cook until the bread is browned on both sides.
3. Enjoy!

This recipe is very easy to make and the onion and tomato slices can easily make up to four sandwiches, so you may want to cut the onion and tomato in half and save the other halves for later.