Preheat oven to 375 degrees F.

Using a 2 ½ inch cookie cutter cut circles in the sliced Italian bread. Melt 2 tablespoons of the butter and lightly brush the tops of each circle of bread. Place on a large cookie sheet and bake for 4 minutes.

Meanwhile, using the same cookie cutter, cut slices of cheese into circles.

If using diced onions, melt butter in a medium frying pan over medium heat and saute until the onions are soft and just starting to brown.

Mix ground beef, ketchup, mustard, salt and pepper in a large bowl. Scoop ¾ to 1 tablespoon of ground beef mixture onto the top of each toasted bread circle. Press ground beef into a thin layer on the bread circles. Top with a little sauteed onion, if using, and cheese circles.

Bake for 7-10 minutes and serve immediately.