When I'm extremely lazy and want to make something that will last me a couple meals, I resort to this recipe from Smitten Kitchen, a blog that Special K and I follow adamantly. This woman has the most amazing recipes and photographs. Go check out her blog! This sauce is seriously the easiest to make, and it's quite delicious. Here's her recipe (I simplified and added things in some cases):
Serves 4-5
28 ounces (800 grams) whole peeled tomatoes or tomato puree from a can (She likes San Marzano, but you can really use any brand)
5 tablespoons (70 grams or 3/4 a stick) unsalted butter
1 medium-sized yellow onion, peeled and halved
Salt to taste (maybe)
Throw the tomatoes or puree, butter, and onion in a sauce pan over medium heat. Bring the sauce to a simmer then lower the heat to keep the sauce at a slow, steady simmer for about 45 minutes, or until droplets of fat float free of the tomatoes. Stir occasionally, crushing the tomatoes against the side of the pot with a wooden spoon. If you are using whole tomatoes, CRUSHCRUSHCRUSH. Otherwise, your sauce will be less saucy and more tomato chunky. Remove from heat. She prefers to discard the onion, but I'm a fan of leaving it in. Add salt to taste if you please. However, most tomatoes came salted, so you don’t really need to add more. Keep sauce warm while you prepare the pasta.
Serve with spaghetti or your choice of pasta. It tastes good with or without parmesan cheese, so it's up to you what you prefer. Bon appetite. :)