tomato sauce with onion and butter

http://smittenkitchen.com/blog/2010/01/tomato-sauce-with-butter-and-onions/
Excerpt:

“I could no longer resist this sauce, and frankly, I don’t know why I even tried to: food bloggers obsess over it, and they’re not a bad lot to base a recipe selection upon. Adam of Amateur Gourmet fell for it five years ago.”