Add everything to the slow cooker, stir. Cover and cook on LOW for 8 hours or HIGH for 4 hours, without opening the lid during the cooking time.
After the sauce is done cooking you can use right away. Or, uncover and let cool for about an hour before ladling into freezer storage bags. Plastic or glass jars can be used, the same way you would with freezer jam, leaving room at the top for the sauce to expand.
Freeze for up to 3 months.
To use, place the bag of sauce in the fridge to thaw the day before the sauce is needed.
Can I use fresh herbs?You can always use fresh herbs if you have them on hand. I prefer to stick with dried spices because they store better and are less expensive. Feel free to add up one teaspoon of your favorite herb or spice such as rosemary, thyme, oregano, or basil at the same time that you add in the onion powder and salt.