Pour ground tomatoes into a slow cooker.

Swirl 1/4 cup water in each emptied can and pour into the slow cooker.

Add sugar, vinegar, onion powder, garlic powder, salt, celery salt, mustard powder, black pepper, and whole clove to the slow cooker.

Whisk to combine all ingredients in the slow cooker.

Cook on high, uncovered, until the mixture is reduced by half and very thick (10 to 12 hours).

Stir the mixture every hour or so during cooking.

Smooth the texture of the ketchup using an immersion blender for about 20 seconds.

Ladle the ketchup into a fine strainer.

Press the mixture with the back of a ladle to strain out any skins and seeds.

Transfer the strained ketchup to a bowl.

Cool completely before tasting and adjusting salt, black pepper, or cayenne pepper to taste.