In a large heavy bottomed sauce pot or dutch oven, bring the oil up to medium heat. Add in the onions and cook for 6-8 minutes or until lightly golden and fragrant. Add in the garlic and cook for 2 more minutes then add in the thyme. Make sure to stir so the garlic doesn't burn.
Add in both cans of tomatoes. I use a little water (about 3 tbsps.) in each can to get the remaining tomatoes out. Season the mixture with a couple large pinches of salt and a good amount of pepper. Add in the basil, stir and cover with lid.
Let the sauce cook for 3 hours on low, or all day if you have the time, stirring occasionally to prevent sticking and burning.
After the sauce has cooked for at least 3 hours, remove from heat and let cool slightly.
Using an immersion blender or a tabletop blender puree the sauce until velvety smooth. Place back into a clean pot.
Turn the heat back onto low, and slowly stir in the cubed butter. Check for seasoning adding more salt and pepper if needed. Add 1-2 tbsp. of sugar if the sauce tastes too acidic.
Serve over pasta, as a pizza sauce, with bread or in soups.
Recipe Courtesy of Megan Mitchell