Mix together all ingredients, except bread. Cut the crusts off very fresh bread slices. Butter 1 side only; with buttered side down, line muffin tins with bread slices, making sure you don't break the bread at the bottom. Fill each muffin cup with a good tablespoon of hamburger filling. Bake at 180ºC for 30 mins. They can be frozen, then reheated, or can be served cold. I use a lean ground beef.