Chop the aromatics
Peel all 4 cloves of garlic, then mince 2 cloves very finely for the meatballs and slice the other 2 for the sauce. Finely chop the onion and the flat-leaf parsley, keeping 1 tablespoon of parsley aside for the finish.
Soak and mix
Tear the day-old white bread into a bowl and pour over the whole milk. Let it soak for 5 minutes until soft and pillowy, then mash it with a fork. Add the ground beef, ground pork, egg, minced garlic, chopped parsley, salt, and pepper, and mix with your hands until everything is evenly combined.
Shape and dredge
Scoop up portions of the mixture and roll them into walnut-sized balls. Dredge each one lightly in the all-purpose flour, then set them on a tray and tap off any excess.
Fry the meatballs
Heat the olive oil in a large skillet over medium-high. Fry the meatballs in batches for 8 minutes, turning them often until they are browned on several sides and just firm enough to hold their shape, then transfer them to a plate. Don't crowd the pan; give each meatball a little space so it browns instead of steaming.
Build the sauce
Pour off all but a thin film of fat, then add the extra virgin olive oil to the same pan. Cook the onion over medium heat until soft and translucent, about 5 minutes, then stir in the sliced garlic and sweet paprika for 30 seconds so the spice blooms without burning. Pour in the dry white wine and scrape up any browned bits from the pan, then add the crushed tomatoes, chicken stock, bay leaf, and sugar. Season lightly with salt and pepper and simmer for 10 minutes.
Simmer together
Slide the meatballs and any juices back into the sauce. Spoon sauce over the top, lower the heat, and simmer gently, partly covered, for 12 minutes until the meatballs are cooked through and the sauce is glossy and thick enough to coat a spoon.
Garnish and serve
Remove the bay leaf, taste the sauce, and adjust salt and pepper if needed. Spoon the albóndigas into warm bowls, ladle over plenty of sauce, and finish with the reserved parsley.
