You can also go very simple and use Hazan's recipe.
1 can peeled plum tomatoes (You can use fresh tomatoes but it isn't really necessary.)
half a stick (or a bit more) of butter (you should slice it up some)
an onion (or some shallots). Slice it in half or quarters. Don't go smaller than that.
Put everything in a pot. Break up the tomatoes.
If the butter isn't salted, add some salt to taste.
Cook over medium heat until it bubbles, then lower the heat and let it simmer.
Let the liquid reduce down to basically nothing. (~45 minutes, but other than stepping in and stirring it every 10 minutes or so, you don't have to do anything.)
Lovely base for anything else you want to do with a basic red sauce.
