How to Make It
Preheat oven to 450°F. Place cauliflower stems and florets on a rimmed baking sheet. Drizzle with oil, and toss to coat. Bake in preheated oven until tender-crisp but not yet browned, about 10 minutes. Cool completely, about 20 minutes.
While cauliflower cools, stir together celery, scallions, mayonnaise, sour cream, dill, parsley, mustard, vinegar, and sugar in a large bowl. Add cauliflower, bacon, eggs, salt, and pepper, and toss to coat. Serve immediately, or chill until ready to serve.