Instructions:
- Cook the Vegetables:
- In a large, heavy-bottomed pot, combine the chopped tomatoes, onions, and bell peppers.
- Cook over medium heat, stirring occasionally, until the vegetables are soft and the tomatoes release their juices, about 30-40 minutes.
- Remove from heat and let the mixture cool slightly.
- Blend the Mixture:
- Working in batches, transfer the cooked tomato mixture to a blender or food processor and blend until smooth. Be careful as the mixture will be hot.
- Strain the Mixture:
- Strain the blended mixture through a fine-mesh sieve into a clean pot to remove seeds and skins, pressing with a spoon to extract as much liquid as possible.
- Add Seasonings and Simmer:
- Add both vinegars, brown sugar, salt, mustard seeds, allspice, cloves, cinnamon, black pepper, and cayenne pepper to the strained tomato mixture.
- Bring the mixture to a boil over medium-high heat, then reduce the heat to low and simmer uncovered, stirring occasionally, until the ketchup thickens to your desired consistency, about 2-3 hours.
- Prepare for Canning:
- Sterilize canning jars and lids according to manufacturer’s instructions.
- Ladle the hot ketchup into hot, sterilized jars, leaving 1/2-inch headspace. Wipe the jar rims clean with a damp cloth.
- Seal the jars with sterilized lids and rings.
- Process the Jars:
- Process the jars in a boiling water bath for 15 minutes (adjust time based on your altitude if necessary).
- Remove the jars from the water bath and let them cool completely. Check the seals and store in a cool, dark place for up to 1 year.