1. Bring a large saucepan of water to a boil over high heat; add a generous amount of salt. Add cauliflower, and cook until crisp-tender, about 3 1/2 minutes. Using a slotted spoon, transfer to a large heatproof bowl. Repeat with carrots, cooking about 2 1/2 minutes, and then with celery, cooking about 2 minutes; combine with the cauliflower.

2. In a medium saucepan over high heat, combine 2 cups water with vinegar, peppercorns, bay leaves, garlic, sugar, and 3 tablespoons salt. Boil until salt and sugar have completely dissolved, about 2 minutes. Immediately pour over vegetables, and gently stir in pepperoncini.

3. Let cool completely. Place in an airtight container, and refrigerate at least 1 hour and up to 1 week. Discard bay leaves. Serve chilled or at room temperature.