In your stand mixer, place bread cubes and pour milk/vinegar over the bread cubes.
Mix together, so the bread cubes are evenly coated in the milk/vinegar or buttermilk.
Let sit for 10 minutes while you prep the rest of your ingredients.
To the stand mixer, add in the finely minced yellow onion, pressed garlic, parmesan, egg yolks, and spices.
Mix until well combined.
Using your hands, combine the finely minced bacon, ground beef, and ground pork.
With your stand mixer running, add in 1/3 of the bacon/beef/pork mixture. Once combined, add in another 1/3 of the mixture, and again, once combined, add in the last 1/3.
Once fully combined, store the meatball mixture, covered, in the refrigerator until ready for use.
Preheat broiler on high and place rack on the top rung.
Using a large cookie scoop (mine is about 3 tablespoons or 1.5 oz), scoop out your meatballs (you should end up with 36) onto a silicone lined baking sheet.
Broil for 8 minutes, rotating the pan 180 degrees halfway through (keep an eye on them as broiler temperatures can vary). The tops should be nicely browned and the internal temperature should be about 160 degrees F.
Place the meatballs into your crockpot (it should have an hour left of cook time), and cover the meatballs with the sauce.
Set the crockpot to HIGH and cook for an additional hour.