Bring a large pot of salted water to boil.
Cook linguine until al dente. Reserve ½ cup pasta water, then drain.
Heat olive oil in a large pan over medium heat.
Add ground beef and Italian sausage. Break apart with a spatula until browned.
Stir in onion, garlic, chili flakes, and Italian seasoning. Cook until onions are soft.
Season with salt and pepper. Remove meat mixture and set aside.
In the same pan, melt butter over medium heat.
Add garlic and cook until fragrant (about 1 minute).
Add reserved pasta water and stir.
Add cooked linguine to the garlic butter sauce.
Stir in Parmesan and mozzarella until creamy and cheesy.
Fold in the beef and sausage mixture.
Toss until pasta is fully coated.
Garnish with fresh parsley and extra Parmesan.
Serve hot with garlic bread or a side salad.
