Turn on oven to 350 degrees. Grease a baking dish with shortening. Save until Step 4.
Tear the bread into pieces and put in blender container. Cover the blender; blend on high speed until crumbs form (you should have about 1 1/2 cups). On cutting board use a sharp knife to cut onion into very small pieces (you should have about 1/2 cup).
Crack the eggs into a large bowl. Beat with a fork or whisk until yolks and whites are mixed. Add bread crumbs, onion, milk, 1 teaspoon of the mustard, and pepper. Add ground ham and ground pork. Mix well with wooden spoon.
Place a piece of waxed paper on the counter or table. Put the meat mixture on waxed paper. Use your hands to divide the mixture into 12 portions. Shape each portion into a ball. Place the meatballs in the prepared baking dish.
In a small bowl stir together brown sugar, catsup, vinegar, and the remaining 1 teaspoon mustard. Stir until sugar is dissolved. Pour over meatballs.
Put the baking sheet in the oven. Bake about 35 minutes or until internal temperature is 160 degrees F. Turn off oven. Use hot pads to remove baking dish from oven. Use a large spoon to serve meatballs. Stir sauce in dish. Spoon sauce over meatballs to serve.
Serve with corn on the cob, dinner rolls, and milk.