Prepare the cabbage and carrots. Halve the cabbage through the core, then remove the tough, white core from each half. Using a sharp knife, shred the cabbage into thin ribbons — you should hear a clean, crisp snap as you cut through each leaf. Grate the carrots on the large holes of a box grater; the shreds should be bright orange and moist, with a sweet, earthy aroma.

Salt the vegetables. Place the shredded cabbage and grated carrot in a large colander set over a bowl. Sprinkle the fine sea salt evenly over the top and toss gently with your hands. Leave this to sit for 30 minutes. You will notice the vegetables begin to release their water — the bowl beneath will slowly fill with a pale, cloudy liquid, and the cabbage will soften slightly, becoming more pliable and less stiff.

Rinse and dry thoroughly. After 30 minutes, rinse the salted vegetables under cold running water to remove the excess salt. Shake the colander well, then transfer the vegetables to a clean tea towel. Gather the corners of the towel and twist firmly, squeezing out as much remaining moisture as you can. The cabbage should feel dry to the touch, not damp, and the towel will be noticeably wet. This step is crucial for a creamy, not watery, slaw.

Slice the red onion. Cut the red onion half into very thin half-moons. As you slice, the sharp, pungent scent of fresh onion will fill the air. Place the slices in a small bowl of cold water for 5 minutes — this tames their bite while keeping their beautiful purple hue. Drain and pat dry.

Whisk the dressing. In a small bowl or a jar with a tight-fitting lid, combine the mayonnaise, apple cider vinegar, caster sugar, celery seeds, black pepper, and mustard powder. If using buttermilk, add it now. Whisk or shake vigorously until the sugar has dissolved and the dressing is pale, creamy, and smooth. Taste a tiny bit — it should be tangy with a subtle sweetness, and the celery seeds should provide a gentle, herbal warmth.

Combine everything. In a large salad bowl, add the dried cabbage and carrot mixture along with the drained red onion. Pour the dressing over the top. Using two large salad servers, toss the vegetables thoroughly, ensuring every strand is coated. The sound of the dressing coating the cabbage should be a soft, slick rustle, not a wet splash. I used to struggle with this dish until I discovered this technique of salting and drying — now the dressing clings like a dream.

Rest before serving. Cover the bowl with cling film and place it in the refrigerator for at least 1 hour. During this time, the flavours will deepen and marry together. The cabbage will soften just slightly while still retaining its essential crunch. My husband, who's usually picky, asked for seconds the first time I made it this way!