Heat the olive oil in a skillet over medium heat and cook the onions until they are soft and translucent. Add in the Italian sausage and fry until the sausage is browned, about another 10 minutes.
Place the sausage and onions in your slow cooker.
In the same skillet, add the ground beef, Italian seasoning, minced garlic and marjoram. Cook until the meat is browned, making sure to break the beef into chunks ( this will be in your sauce remember). Drain and place the ground beef into the slow cooker.
Stir in the tomato sauce, tomato paste, diced tomatoes, stewed tomatoes, thyme, basil, oregano and sugar.Set your slow cooker on low and cook the sauce for 10 hours. Serve over your favourite spaghetti noodle or other pasta!
Nutrition is an automatic estimate and will vary with the brands you use.
Recipe from https://fastandslowcooking.com/meat-lovers-slow-cooker-spaghetti-sauce/