In a large mixing bowl, combine the ground beef (or half beef and half pork), egg, breadcrumbs, grated Parmesan, chopped parsley, minced garlic, salt, and black pepper. Mix gently until combined and form into 1-inch balls, yielding about 20-24 meatballs.

Heat olive oil in a skillet over medium heat. Once shimmering, add the meatballs spaced apart. Sear for 6-8 minutes until browned on all sides, then remove and set aside.

In the same skillet, melt unsalted butter over medium-low heat. Add the remaining minced garlic and red pepper flakes (if using) and cook for 1-2 minutes until fragrant. Stir in lemon juice and return the meatballs, simmering for 5-7 minutes.

While simmering, cook the linguine in boiling salted water according to package instructions, usually 8-10 minutes. Reserve about ½ cup of pasta water and then drain.

In another saucepan, melt butter over medium heat and stir in heavy cream. Add reserved pasta water gradually, whisking until smooth. Stir in Parmesan and season with salt and black pepper. Toss linguine in the sauce.

Serve by placing creamy linguine on each plate and topping with meatballs. Drizzle remaining garlic butter sauce over the top and garnish with parsley and Parmesan.