Cucumber Ketchup

3 very large cucumbers - peeled, seeded, and chopped

2 large onions, chopped

½ cup salt

1 cup apple cider vinegar

¼ cup mustard seed

1 teaspoon ground black pepper

Mix cucumbers and onions in a large bowl; stir in salt until thoroughly combined. Transfer mixture to a colander, cover colander with plastic wrap, and let drain overnight.

Place drained vegetables into a large bowl and pour in apple cider vinegar; stir to combine. Working in batches if necessary, place vegetables with vinegar into a blender and puree. Pour puree into a bowl and season with mustard seed and black pepper. Spoon the ketchup into small jars with lids; cover and store in refrigerator for 3 days before serving. Ketchup keeps well in the refrigerator.