This isn't a quick recipe, but it is simple. Just tomatoes, butter, onion, and garlic. Molly's sauce calls for the tomatoes to be chopped before cooking, resulting in a chunkier sauce. I prefer mine smooth so I blend it (like she describes here), but if you like it with more texture you can skip the last step of reducing the sauce. I also added some garlic to my version, which wasn't in the original, but I think makes it even better. San Marzano tomatoes are perfect for this recipe but if you can't find any, or if they're too expensive, other good quality varieties like Muir Glen work great.
Tomato Sauce with Butter and Onion
adapted from Orangette and Marcella Hazan
2 cups whole, peeled, canned plum tomatoes, with their juices (about one 28-oz. can)
5 Tbsp. unsalted butter
1 medium yellow onion, peeled and cut in half
2 cloves garlic, peeled and smashed but not chopped
Salt, to taste
Combine the tomatoes, their juices, the butter, the garlic and the onion halves in a medium saucepan. Add a pinch or two of salt. Place over medium heat and bring to a simmer. Stir occasionally, mashing tomatoes with the back of a wooden spoon. Cook, uncovered, at a very slow but steady simmer, adjusting the heat as necessary, for about 45 minutes, or until droplets of fat float free from the tomato.
Remove onion and discard. Blend tomatoes and garlic with a stick blender (or in a food processor or blender, in batches) until smooth. Return sauce to pan and simmer until the thickness of the sauce is to your liking.
Taste and salt as needed.
Makes enough sauce for about 1 pound of pasta, or 4 servings