In a small saucepan combine vinegar, cloves, cinnamon, allspice and celery seed. Bring to a boil over high heat, then remove from heat and set aside to cool.
(This step is optional but I recommend it if you don’t have a food mill) - cut a small “X” into the bottom of each tomato and dip them into boiling water to loosen the skins. Transfer to an ice water bath, then peel and core and quarter the tomatoes.
Place the cored and quartered tomatoes, onions and cayenne pepper into a large pot and bring to a boil. Reduce the heat and simmer for 20 minutes. Put the tomato mixture through a fine mesh sieve or a food mill, reserving the juice and discarding the solids. Return the juice to the pot. Strain the vinegar mixture through a mesh sieve lined with cheesecloth (or a coffee filter if you don’t have cheesecloth) and add it to the tomato mixture. Boil the sauce for 1- 1 ½ hours or until the sauce has reduced down to a very thick ketchup – consistency.
Ladle into 2 hot pint jars and process for 15 minutes in a boiling water bath or keep in the fridge and use within a month.