In a large mixing bowl, combine ground beef, sausage, egg, breadcrumbs, 1/4 cup heavy cream, parsley, salt and pepper, and sage. Mix well. Form into 1 inch balls. Brown meatballs in batches in large skillet over medium high heat for 5-6 minutes per side or until cooked through and well browned on all sides. Place meatballs in crock pot (medium high) until all batches of meatballs are cooked. Reduce stove heat to medium low. Whisk flour into drippings. Gradually and slowly add cream. Heat until bubbly. Add sour cream. Heat through. Pour over meatballs in crockpot. Simmer on low for four to five hours.