Let’s start pickling today!
Set aside three tablespoons of the vinegar.
Pour the rest of the vinegar in a large pot, add sugar, mustard powder, and all the other ingredients except the cornstarch. Bring everything to a simmer.
Whisk the remaining vinegar with the cornstarch until you get a smooth paste. Stir this into the simmering liquid to make it creamy.
Fold in the drained veg, heat for 4-5 minutes, stirring constantly, until the veg are no longer raw.
While still hot, place in sterile jars and fill to the top with more brine.
Twist the lids on and turn them upside down for 5 minutes to sterilize them.
Turn it upside down, let it cool down, and store it in the fridge for best results.
Piccalilli will keep for up to 3 months!