Keep the beef cold. Keep the ground beef refrigerated until mixing. Dice the peeled onion very finely, no larger than about 1/16 inch (2 mm), and finely grate the garlic. Measure the meatball seasonings separately from the sauce seasonings.
Mix the meatballs. Combine the cold beef, onion, garlic, egg, breadcrumbs, and meatball salt, paprika, and pepper. Add the ice-cold water in two additions. Mix with clean hands for about 3 minutes, just until evenly distributed and lightly cohesive, without squeezing into a hard paste. Do not taste the raw mixture.
Chill the mixture. Cover and refrigerate for 30 minutes at 40°F (4°C) or below. Wash hands, utensils, and work surfaces after contact with raw beef. Keep the mixture cold while preparing the pan and sauce ingredients.
Shape according to servings. Make four equal meatballs for every serving shown in the card. Weigh the mixture and divide it evenly so the meatballs stay about the same size at every batch setting, roughly 1.9 oz (54 g) each. Round gently with damp hands, pressing only enough to close large cracks. Place on the raw-food tray and refrigerate until browning.
Brown in uncrowded batches. Preheat a deep skillet over medium-high heat for about 3 minutes. Divide the listed sunflower oil among the browning batches, using a little more for the first round if needed. Brown only as many meatballs as fit with space to turn, for 4–5 minutes per batch, carefully turning to color several sides. Keep waiting meatballs refrigerated. The centers are not cooked through yet. Transfer browned meatballs to the raw-food tray, which must not be used unwashed for the finished dish. Do not add another oil allowance for the sauce.
Build the mild sauce. Reduce the heat to medium. Stir the tomato paste into the pan for about 1 minute. Stir in the sauce paprika for no more than about 10 seconds, then immediately add the passata and sauce water. Add the sauce salt, pepper, and bay. Stir and bring to a gentle simmer, then simmer uncovered for 5 minutes.
Simmer the meatballs covered. Return the browned meatballs to the gently simmering sauce, preferably in a single layer. Spoon sauce over them, cover, and simmer gently over low to medium-low heat for about 25 minutes. Turn carefully after about 12 minutes. Avoid a rolling boil, which can break them. Reduce heat if sauce catches; do not add water automatically while enough liquid remains. For larger batches, divide meatballs and sauce among additional comparable pans.
Verify the safe center temperature. Insert a clean food thermometer into the center of several of the largest meatballs, avoiding the pan bottom. Every checked center must reach at least 160°F (71°C), the USDA ground-beef minimum. Do not judge safety by color alone. If needed, cover and cook for another 3–5 minutes, then check again. Wash a probe that touched undercooked meat before rechecking cooked food.
Finish and serve. Remove the bay leaf. If the sauce is still very thin, lift fully cooked meatballs onto a clean plate and simmer the sauce uncovered for 2–3 minutes, then return them. Serve four meatballs per person with an equal share of the prepared sauce. Use clean utensils and dishes that have not touched raw or partly cooked beef.