In a bowl, combine egg yolk, ground beef, onio , salt
and pepper. Shape mixture by teaspoonfuls into 24
balls. Remove crusts from bread; roll flat and ut into
1 - 1/2 inch rounds. Place meatballs on bread rounds;
make a depression in each ball and fill with a cube of
cheese, making sure bread is coverd with meat mixture.
Place on baking sheet. Broil in preheated oven about 5
inches from heat 3 - 5 minutes or until no pink
remains. Garnish with ketchup, mustard, sliced green
onions or sliced dill pickles if desired.
