In a large saucepan, combine the chopped tomatoes and finely chopped onion. Cook over medium heat until the tomatoes have softened and released their juices, stirring occasionally.
Using a blender or an immersion blender, puree the cooked tomatoes and onions until smooth.
Return the tomato mixture to the saucepan and add apple cider vinegar, brown sugar, salt, garlic powder, onion powder, ground cloves, ground cinnamon, and ground allspice.
Stir well to combine and bring the mixture to a simmer over medium heat.
Reduce the heat to low and let the ketchup simmer uncovered for about 1 hour, stirring occasionally, until it thickens to your desired consistency.
Once thickened, remove the saucepan from heat and let the ketchup cool down.
Transfer the homemade tomato ketchup to sterilized jars or airtight containers for storage.
