Step 1

1 Cut the fresh tomatoes in half lengthwise

Step 2

2 Place them cut side down in a wide saucepan; cover and cook over medium-low heat for 10 minutes, until slightly softened

Step 3

3 Working in batches as needed, transfer the tomatoes to a hand-cranked food mill set over a mixing bowl

Step 4

4 Puree until the solids are completely broken down, with tomato seeds and skins left in the mill

Step 5

5 Discard the solids; pour the pureed tomatoes and juices back into the saucepan, then add the butter and onion halves, cut sides down

Step 6

6 Cook over medium heat until the butter has melted, then season lightly with salt and add the sugar, if using

Step 7

7 Reduce the heat to medium-low; cook (uncovered) for about 45 minutes, stirring occasionally, to form a smooth, brightly colored sauce that has thickened a bit

Step 8

8 Taste, and season with salt, if desired

Step 9

9 Discard the onion before serving or storing

Step 10

10 NOTE: If you use canned tomatoes, chop, squish or puree them

Step 11

11 Then, add them and their juices to the saucepan and cook as directed with the other ingredients

Step 12

12 If you don't have a food mill and want to use fresh tomatoes, peel and de-seed them first

Step 13

13 Here's how: Slice an X through the base and dunk them in boiling water for 30 seconds to 1 minute, or until they float to the surface

Step 14

14 Lift them out with a slotted spoon and place them in a bowl of ice water

Step 15

15 This will make them easy to peel

Step 16

16 After peeling, slice the tomatoes in half and, using your fingers, scoop out and discard the seeds and gel

Step 17

17 Tear the tomatoes into pieces and run them through a food processor, in batches if necessary, to puree