Tall stockpot with a lid and silicone trivet for processing
Wide-mouth canning funnel
Clean kitchen towel
Medium nonreactive bowl
Large nonreactive bowl
Heavy-bottom preserving pot
In a large bowl, use a wooden spoon to stir together the chopped cabbage, cauliflower, tomatillos, onions, poblano peppers, and sea salt. Let the mixture sit for 4 hours, as the salt draws moisture out of the vegetables.
After 4 hours, take the chopped vegetables a handful at a time and squeeze them to extract as much liquid as possible. Do not rinse. Reserve the squeezed veggies in a medium nonreactive bowl.
Combine the vinegar, sugar, mustard seed, ground mustard, and turmeric in the stainless saucepan and bring to a boil over high heat. Stir to dissolve the sugar and salt. Once the sugar and salt dissolve, add the vegetables and return to a boil. Reduce heat. Simmer for 10 minutes.
Remove from the heat and use a slotted spoon to transfer the relish to the prepared jars. Pour the brine (the remaining liquid) over the relish to cover, leaving ½ -inch headspace. Remove air bubbles and wipe rims. Place the lids on the jars and screw on the bands until they’re fingertip tight.
Process in a water-bath canner for 10 minutes, adjusting for altitude if needed. After 24 hours, check the seals. Label, date, and store out of direct sunlight without the bands for up to a year.