How to Make It
In a small bowl, mash the garlic with a large pinch of salt. Whisk in the olive oil and mustard, then whisk in the buttermilk in a thin stream. Add the herbes de Provence and a pinch of pepper and let the dressing stand for 30 minutes.
Meanwhile, steam the broccoli florets until crisp-tender, about 5 minutes. Plunge the florets into a bowl of ice water. Drain well and pat dry.
In a medium skillet, cook the bacon over moderately high heat until browned, about 5 minutes; drain.
In a large bowl, toss the broccoli florets and stems with the sliced onion and the dressing. Sprinkle with the Roquefort and bacon and serve.