Preheat oven to 400˚F. Divide 2 pounds of beets between 2 pieces of foil; bring edges together and crimp to make packets. Roast until the beets are just tender when pierced with the point of a knife, about 1 ¼ hours. Unwrap the beets and let them cool.
Meanwhile, whisk ¼ cup oil, 2 tablespoons vinegar, ½ teaspoon mustard, ½ teaspoon honey, ½ teaspoon salt and pepper in a small bowl to make the dressing.
When the beets are cool enough to handle, slip off the skins. Cut into ½-inch cubes and place in a large bowl. Add 1 celery stalk, 1 shallot and the dressing; toss to coat well. Serve at room temperature or chilled.
