►Preheat oven to 400°F with rack in middle.
►Trim any stems off beets and wash beets well. Place them in a roasting pan and drizzle with 1 tablespoon olive oil and 1 teaspoon kosher salt. Add enough water to pan so it comes up the sides about ½ inch. Cover tightly with foil and transfer to oven. Cook for 45 minutes to 1 hour. Beets are done when soft enough to be poked with a paring knife without resistance. Larger ones will take a little longer. Allow them to cool in pan, covered.
►Meanwhile, make the vinaigrette. In a mixing bowl whisk together remaining olive oil, sherry vinegar, water, shallot, whole grain mustard, and 1 tablespoon herbs. Season with salt and pepper to taste, adjusting acidity as needed. Transfer to the fridge.
►When beets have cooled to room temperature, use your hands to peel off skins, with the assistance of a peeler as needed (wear gloves if you don’t want your hands to turn pink). Then slice beets into eighths and transfer to a mixing bowl. Toss with vinaigrette to marinate for at least 30 minutes and up to several hours covered in the fridge.
►To serve, first taste and adjust seasoning as needed, then transfer beets to a serving dish. Top with crumbled Roquefort, toasted walnuts, remaining herbs, a drizzle of olive oil and a touch
of flaky salt if you like.