In a large mixing bowl, combine ground beef, egg, breadcrumbs, grated Parmesan, chopped parsley, minced garlic, salt, and black pepper. Mix gently until just combined, then shape into 1-inch meatballs and set aside.

Heat olive oil in a large skillet over medium heat and add meatballs in batches. Sear for 6-8 minutes, turning until golden brown. Remove and set aside.

In the same skillet, add unsalted butter, minced garlic, and red pepper flakes. Sauté for 1-2 minutes until fragrant. Add lemon juice and chopped parsley, then return meatballs to the skillet to simmer for 5-7 minutes.

Cook linguine according to package instructions, reserving ½ cup pasta water before draining. In another saucepan, melt additional butter, stir in heavy cream, then add grated Parmesan. Thin with reserved pasta water.

Serve creamy Parmesan linguine on plates, top with meatballs and spoon extra garlic butter sauce over them. Garnish with parsley and additional Parmesan.