Combine the beets, 2 tablespoons of the olive oil, 2 tablespoons of the vinegar, and 1 tablespoon of the honey in a vacuum bag or a resealable plastic freezer bag and seal so that there is no air inside the bag.

Assemble the sous vide machine according to manufacturer’s directions and preheat the water bath to 85 degrees C. Lower the bag into the water and cook the beets, fully submerged, until crisp-tender, 2 ½ to 3 hours. Remove from the water and set aside to cool.

When the beets have cooled, transfer the beets to a salad bowl and slice into ¼-inch slices. Transfer the cooking juices from the pouch to a small saucepan. Bring to a simmer and cook until the juices have reduced to about ¼ cup. Add the remaining 1 tablespoon of vinegar, 1 tablespoon of honey, and 1 tablespoon of olive oil and season to taste with salt and pepper.

To serve the salad, place lettuce leaves on salad plates and arrange the beet slices decoratively around the lettuce. Garnish with the feta, pistachios, and mint leaves. Drizzle the plate with the vinaigrette and with additional honey and olive oil.