Step 1

Pour ground tomatoes into slow cooker. Swirl 1/4 cup water in each emptied can and pour into slow cooker. Add sugar, vinegar, onion powder, garlic powder, salt, celery salt, mustard powder, black pepper, cayenne pepper, and whole clove; whisk to combine.

Step 2

Cook on high, uncovered, until mixture is reduced by half and very thick, 10 to 12 hours. Stir every hour or so.

Step 3

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

Step 4

Ladle the ketchup into a fine strainer and press mixture with the back of a ladle to strain out any skins and seeds.

Step 5

Transfer the strained ketchup to a bowl. Cool completely before tasting to adjust salt, black pepper, or cayenne pepper.