Step 1

In a medium saucepan, combine the tomatoes and juices, butter, onion and a pinch or two of salt.

Step 2

Place over medium heat and bring to a simmer.

Step 3

Cook, uncovered, at a steady simmer for 45 minutes.

Step 4

Stir occasionally, mashing any large pieces of tomato with the back of a wooden spoon.

Step 5

Remove onion before serving.