Add the tomatoes, onions, garlic, jalapeños (if using), basil, parsley, oregano, thyme, crushed red pepper, salt and pepper and 1 tablespoon butter to the bowl of a crockpot. Cover and cook on low for 7 to 8 hours (or 3-4 hours on high) stirring once or twice if possible. After 8 hours remove the onion if you wish (I do, but some people love it left in). Use the back of a spoon or a potato masher to break down the tomatoes. If you like a smooth sauce use an immersion blender to puree the sauce or transfer to a blender or food processor and then return the sauce to the crockpot, leaving the lid off.