In a saucepan, combine the chopped tomatoes and onions.
Cook over medium heat until the tomatoes break down, about 10 minutes.
Add apple cider vinegar and stir well.
Mix in the brown sugar, salt, and spices.
Let the mixture simmer for 20 minutes, stirring occasionally.
Remove from heat and let cool slightly.
Blend the mixture until smooth using an immersion blender or regular blender.
Return the blended ketchup to the saucepan.
Simmer for an additional 10 minutes to thicken.
Allow to cool completely before transferring to a jar.