Bring a large pot of salted water to a boil. Add the cauliflower and cook just until fork-tender, about 8 minutes. Drain well, then spread in a single layer onto a clean kitchen towel to absorb excess moisture and release steam quickly. Let the cauliflower sit for 10 minutes, until cooled to room temperature. (Letting the cauliflower sit for a few minutes makes all the difference in keeping the salad creamy and not turning watery.)

In a large bowl, whisk together the mayonnaise, Dijon mustard, kosher salt, black pepper, and pickle juice until smooth.

Add the cooled cauliflower, red onion, celery, chopped pickles, and fresh dill. Stir gently until everything is evenly coated.

Cover and refrigerate for at least 2 hours, or up to 24 hours. The flavor only gets better as it sits and is even better the next day.

Adjust seasoning to taste and serve cold.