Heat a large Dutch oven or pot over medium-high heat. Add ground beef and Italian sausage, and cook 8 to 10 minutes or until cooked through, breaking up meat with wooden spoon as it cooks. Use slotted spoon to transfer meat to medium bowl.

Drain all but 1 tablespoon fat from pot and reduce heat to medium. Add onion and cook 4 to 5 minutes or until softened, stirring occasionally. 

Add garlic, tomato paste, oregano, parsley, salt, black pepper and red pepper flakes, and cook 1 minute, stirring constantly. 

Add meat back to pot and stir in marinara sauce and stock.

Heat to simmering over medium-high heat; stir in noodles. Cook 10 to 12 minutes or until noodles are al dente, stirring frequently. 

Reduce heat to low. Stir in cream; cook 6 to 8 minutes or until noodles are tender. Serve soup garnished with ricotta, Parmesan and basil, if desired.

Heat large skillet (or stovetop-safe slow cooker insert) over medium-high heat. Add ground beef and Italian sausage; cook 8 to 10 minutes or until cooked through, breaking up meat with wooden spoon as it cooks.

Drain excess fat from meat mixture and transfer meat mixture to bowl of 5-quart or larger slow cooker. Add garlic, onion, tomato paste, oregano, parsley, salt, black pepper, red pepper flakes, marinara sauce and beef stock; stir well. Cover and cook on high 3-1/2 hours or low 7-1/2 hours.

Stir in noodles. Cook on high 20-30 minutes longer or until pasta is tender.

Stir in cream. Serve soup garnished with ricotta, Parmesan and basil, if desired.