Piccalilli is a traditional British mixed vegetable relish characterized by its tangy, slightly spicy mustard sauce. This vibrant condiment combines chopped cauliflower, shallots, cucumbers, green beans, and optional carrots, all pickled in a flavorful blend of apple cider vinegar, turmeric, mustard powder, and other aromatic spices. Perfect for adding zest to sandwiches, cold meats, and cheeses, this recipe allows the vegetables to soak and simmer before thickening the sauce with flour, resulting in a perfect balance of crunch and tang.