Add the drained tomatoes, the 2 other cans of tomatoes (juice and all), the onion, garlic and butter to the crockpot. Cover and cook on low for 6-8 hours, stirring occasionally if desired. The tomatoes will break down but near the end, I like to take a potato masher and crush them as much as I can. I prefer to remove the onion, but my husband likes to keep it in there, so it’s your choice! Season with salt and pepper, then taste and season additionally if needed. Sometimes I need to add a little more salt and pepper. You can also add some dried oregano or basil if you’d like. Use as desired on pasta, pizza, casseroles, etc. This is a very simple, fresh-tasting tomato sauce. If you’re a tomato sauce connoisseur, it may not be for you – add whatever you’d like to make it your own!