If possible sauté the onions and garlic in about 3 tablespoons oil in a small skillet before adding to the crock pot, if not then just omit the oil, which will make this marinara sauce pretty much fat-free! You will need a minimum of 4-quart crockpot for this recipe. The longer you cook this sauce on low heat the thicker and richer it will be! but it can also be cooked on high-heat setting for about 5 hours if you want a quicker sauce, I strongly suggest to cook it for a longer time! If desired you can double the recipe, this sauce freezes very well!