Thick spaghetti sauce takes patience. Start with stewed tomatoes and add some tomato paste. The paste will help to thicken it up a bit. Add salt, sugar, pepper and spices to taste. I usually use thyme, oregano, marjoram, garlic powder, and basil. You can add onions, or use onion powder. You can add meat if you like. This is an all day kind of project. It will take time to cook it down. Once the thickness is to your liking, sit down, and enjoy a plate of your favorite pasta. We enjoy spaghetti sauce or burgers too.