In a large bowl soak bread slices in the milk for 3-5 minutes.
Then add the ground beef, eggs, chopped onion, baking powder, salt, and pepper. Mix to combine.
With the help of a cookie scoop, form mixture into 1 to 2-inch meatballs. Place on a parchment lined cookie sheet and freeze for 30-45 minutes.
When slightly firm, working in batches, brown the meatballs in a large skillet then place into a 2 ½ to 3-quart baking dish.
Once all meatballs have been browned (don’t worry if not completely cooked through, they will finish in the oven), mix up the sauce by combining the cream of mushroom and cream of chicken soup with the 1 cup of milk.
Pour sauce over the meatballs in the dish and bake for 1 hour at 350° F.