Make the panade: In a large bowl, combine breadcrumbs and milk. Let sit 3–5 minutes until the crumbs are moistened and soft.

Build flavor in the meatballs: Add eggs, minced onion, half the garlic, Parmesan, parsley, Italian seasoning, red pepper flakes (if using), 1 1/2 tsp salt, and 1 tsp black pepper to the panade. Stir until evenly combined.

Mix in the meat: Add ground beef and pork. Gently mix with your hands or a fork until just combined. Avoid overmixing to keep the meatballs tender.

Shape: With damp hands, form golf ball–sized meatballs (about 1 1/2 inches). You should get roughly 24–28.

Brown (recommended): Heat olive oil in a large skillet over medium-high. Brown meatballs in batches, turning to color on multiple sides, about 5–7 minutes total per batch. Transfer to a plate. Don’t cook through; they’ll finish in the slow cooker.

Start the sauce: In the same skillet, lower heat to medium. Add remaining garlic; sauté 30 seconds. Stir in tomato paste; cook 1–2 minutes to caramelize. Deglaze with beef broth, scraping up browned bits.

Load the slow cooker: Add crushed tomatoes, the skillet mixture, sugar (if using), bay leaves, 1 tsp salt, and 1/2 tsp black pepper to the slow cooker. Stir to combine.

Nestle in meatballs: Place meatballs into the sauce in a single, snug layer. Spoon a little sauce over the top.

Cook low and slow: Cover and cook on Low for 6–7 hours or on High for 3–4 hours, until meatballs are cooked through and very tender (165°F internal temperature).

Finish and serve: Remove bay leaves. Stir in torn basil. Taste and adjust seasoning with more salt, pepper, or a pinch of sugar. Serve with pasta, toasted sub rolls, or polenta. Sprinkle extra Parmesan and parsley on top.