INSTRUCTIONS
1. Place the tomatoes in a tomato press and pass them through the press according to the manufacturer's instructions to remove the seeds.
2. In a blender, process the tomato puree and the onion until smooth, 25 to 30 seconds.
3. In a large saucepan over medium heat, combine the tomato-onion mixture, the vinegar, corn syrup, cayenne pepper, mustard, allspice, ginger, celery seed, cinnamon and clove and stir to mix well. Bring the mixture to a simmer, stirring occasionally, then reduce the heat to medium-low.
4. Continue cooking, stirring occasionally, until the sauce thickens and reduces to about 1 ½ cups, about 1 hour. Be sure to stir more frequently at the end to prevent the ketchup from overcooking and sticking to the bottom of the pan. Season with salt and black pepper, remove from the heat and cool to room temperature. Refrigerate until ready to use.
