In a medium saucepan, combine vinegar, water, salt, sugar, mustard seeds, coriander seeds, and peppercorns. Bring to a boil over medium heat, stirring until the salt and sugar dissolve. Remove from heat and let the brine cool to room temperature to keep the cauliflower crisp.

Cut the cauliflower into even bite-sized florets so they pickle evenly. Set aside while preparing the jar.

Place cauliflower florets into a clean glass jar. Tuck the smashed garlic cloves among the florets, then add the bay leaf along the side of the jar.

Once cooled, pour the brine over the cauliflower until every piece is fully submerged. Use the back of a spoon to gently press down the florets and release any trapped air bubbles.

Close the jar with a tight-fitting lid and refrigerate for at least 24 hours before serving. For a deeper flavor, let it sit for 2–3 days before eating.