Summarize:

Beat the egg using a fork or mini whisk in the bowl first, then add the rest of the ingredients. This way, you will dirty up fewer dishes and have less to clean at the end. Use a wooden spoon or rubber spatula to fold everything together. A great way to make sure that each meatball gets the same amount is to measure everything out with a spoon. Roll the meat mixture into a ball-shape between the palms of your hands. The meatballs can be touching, but they should not be squished or piled on top of each other. Set the baking dish with the meatballs aside when you are done. Add the water, vinegar, sugar, soy sauce, and cornstarch in first, then give them a stir to combine them. Stir them together with a whisk to combine, then add the sliced celery and bell pepper. If you'd like something sweeter, use canned pineapple chunks instead of celery. Stir the sauce often to prevent a skin forming on top. You will notice the sauce thickening as it continues to cook. Once the sauce gets hot, take it off the stove. Gently turn the meatballs with a spoon so that they get evenly coated with the sauce. The meatballs are done when they are no longer pink inside. If they are still not done, bake them for another 30 minutes, or until they are no longer pink inside. White rice is the most common pairing, but you can also use brown rice if you'd like something healthier.
In a large bowl, combine the ground beef, breadcrumbs, onion, allspice, egg, cream and salt. Form the mixture into 1 to 2-inch (2.54 to 5.08 centimeters) meatballs. Arrange the meatballs in a single layer in the bottom of your prepared baking dish. Combine all of the ingredients for the sauce in a medium-sized saucepan. Cook the sauce over medium heat for about 5 minutes. Pour the sauce over the meatballs. Bake the meatballs, uncovered, for 1 hour. Serve the meatballs over rice.