Ingredients

• 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

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Instructions

1. Purée tomatoes (with purée from can) in a blender until smooth.
2. 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).
3. 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).