A very simple and tasty homemade recipe. You can cook your own tomatoes and substitute them for the can of whole tomatoes listed below.
* 1 (28-oz) can whole tomatoes in purée
* 1 medium onion, chopped
* 2 tablespoons olive oil
* 1 tablespoon tomato paste
* 2/3 cup packed dark brown sugar
* 1/2 cup cider vinegar
* 1/2 teaspoon salt
Purée tomatoes (with purée from can) in a blender until smooth.
Cook onion in oil in a 4-quart heavy saucepan over moderate heat, stirring, until softened, about 8 minutes.
Add puréed tomatoes, tomato paste, brown sugar, vinegar, and salt and simmer, uncovered, stirring occasionally, until very thick, about 1 hour (stir more frequently toward end of cooking to prevent scorching).
Purée ketchup in 2 batches in blender until smooth (use caution when blending hot liquids). Chill, covered, at least 2 hours (for flavors to develop).
Cooks' note: Ketchup can be chilled for up to 3 weeks.
Recipe Source: epicurious.com