Place bread cubes in a large mixing bowl; pour milk over bread cubes and let sit for about 6 to 8 minutes, or until the bread has absorbed all the milk.
Using two forks, shred the bread into tiny pieces.
To the bread mixture add grated onions, egg, garlic, beef, pork, salt, pepper, allspice, and nutmeg.
Mix everything together until well combined. It’s best to use your hands to mix it all together.
At this point, you can chill the mixture for 15 to 30 minutes so it’s easier to roll out the meatballs. This is not a must, but it does help.
Form the mixture into about 24 meatballs. Mixture will be wet.
Set a large frying pan over medium-high heat; heat 1 tablespoon butter and 1 tablespoon olive oil.
Working in batches, brown the meatballs on all sides; this should take about 5 to 6 minutes for each batch, depending on the size of the meatballs. Use a spoon to turn them over; turn over gently so they don’t break apart.
Transfer cooked meatballs to a plate and cover with foil.