On a work surface, mash the garlic with a generous pinch of salt until pasty. Scrape the garlic into a bowl and whisk in the buttermilk, yogurt and cider vinegar. Whisk in the canola oil and season the ranch dressing generously with pepper.
In a large, deep pot, bring 1 inch of water to a boil. Set the broccoli in a steamer basket and steam until bright green and crisp-tender, 4 to 5 minutes. Transfer the broccoli to a plate and refrigerate until cool.
Meanwhile, in a skillet, cook the bacon over moderate heat until it's golden and crisp, about 6 minutes. Drain on paper towels.
Arrange the bacon strips on plates and top with the broccoli wedges. Drizzle with the ranch dressing, top with the Roquefort and sprinkle with chives. Serve any extra dressing on the side.