In a large mixing bowl, gently combine the ground beef, finely diced onion, breadcrumbs, and egg, along with half of the minced garlic, salt, and pepper. Mix until just incorporated, avoiding overmixing for tender garlic butter meatballs. Form the mixture into 16 to 18 evenly sized meatballs, about 1 to 1.5 inches in diameter, and set them aside.

Bring a large pot of salted water to a rolling boil. Add the linguine and cook according to package instructions, typically around 8-10 minutes, until al dente. Remember to reserve 1 cup of the starchy pasta water before draining the linguine to aid in creating a creamy sauce later.

In a large skillet over medium-high heat, melt 2 tablespoons of butter until bubbling. Carefully place the meatballs in the skillet and brown them for about 8-10 minutes, turning occasionally, until they develop a golden crust on all sides. Once browned, remove the meatballs from the skillet and set them aside on a plate.

With the skillet still on medium heat, reduce to medium-low and add the remaining 2 tablespoons of butter along with the rest of the minced garlic. Sauté for about 1 minute, or until the garlic becomes fragrant and lightly golden, taking care not to burn it.

Slowly pour in the heavy cream, stirring to combine with the garlic butter mixture. Bring the sauce to a gentle simmer, allowing it to thicken slightly for about 2-3 minutes.

Return the browned meatballs to the skillet, ensuring they are coated in the creamy garlic sauce. Let them simmer for an additional 5 minutes, stirring occasionally.

Add the drained linguine to the skillet with the meatballs and sauce, tossing to combine well. Gradually add the reserved pasta water as needed to achieve your desired sauce consistency.

Remove from heat and sprinkle generously with freshly chopped parsley and additional Parmesan cheese for a final touch. Serve immediately.