In a bowl, combine ground beef, breadcrumbs, milk, Parmesan, egg, garlic, parsley, red pepper flakes, salt, and pepper. Handle briefly—too much mixing can make meatballs dense.

Cover and chill for 15 minutes; this helps the meatballs hold together. Roll into ¾-inch balls, keeping your hands damp to prevent sticking.

Warm a drizzle of olive oil in a Dutch oven over medium-high heat. Add meatballs in batches, browning all sides (about 3 minutes per batch). Transfer to a plate.

In the same pot, sauté 2 more garlic cloves until fragrant, then pour in chicken broth, scraping up browned bits. Bring to a gentle simmer.

Add pasta and cook 5 minutes, then nestle meatballs back into the broth. Simmer until pasta is al dente and meatballs are cooked through, about 6–8 minutes.

Turn off heat, stir in chopped greens and lemon juice; let sit a minute so the residual heat wilts leaves perfectly.

Taste and adjust seasoning. Ladle into bowls, top with extra Parmesan and parsley, and dive right in.