Preheat your oven to 400°F (200°C). Slice the top off the unpeeled heads of garlic, drizzle with olive oil, wrap in foil, and roast for about 30-35 minutes until soft and fragrant.
Once the garlic is cool, squeeze the roasted cloves into a mixing bowl. Add mayonnaise, buttermilk, minced chives, lemon juice, celery salt, and black pepper. Whisk until smooth.
While the garlic roasts, prepare the vegetables: tear romaine, halve grape tomatoes, cut broccoli, and slice cucumber, mushrooms, and red onion.
In a large salad bowl, combine romaine, broccoli, mushrooms, cucumber, tomatoes, and red onion. Toss gently to mix.
Drizzle the roasted garlic dressing over the salad and toss gently to coat. Serve immediately for the best texture.
Enjoy this salad as a side dish or a light meal!