Heat olive oil in a large sauce or sauté pan over medium heat. Add onion and cook, stirring occasionally, until color has faded, or about 7 minutes.Stir in garlic and sauté for one minute. Then add beef, Italian sausage, salt, pepper, and optional red pepper flakes. Break up meat and cook until there are no pink spots left.Stir in marinara sauce. Then add chicken broth and heavy cream and bring to a boil.Once the soup is boiling, add lasagna noodles and cook until tender, 10 to 15 minutes.Remove from heat and stir in Parmesan and mozzarella until melted. Top with basil.