If you don't have an immersion blender, you can add the cooked spaghetti sauce to a regular blender or food processor to blend it. But be careful! The sauce will be hot, and hot food can explode in a regular blender. The safest thing is to let the sauce cool before adding it to a blender or food processor, but if you don't have time for that, make sure you only blend a small amount at a time and vent the top so steam can escape.