2 pounds beets, (5-6 medium)
1/4 cup extra-virgin olive oil
2 tablespoons sherry vinegar, or white-wine vinegar
1/2 teaspoon Dijon mustard
1/2 teaspoon honey
1/2 teaspoon salt
Freshly ground pepper, to taste
1 stalk celery, finely chopped
1 large shallot, finely chopped
Preheat oven to 400°F. Divide 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 1/4 hours. Unwrap the beets and let cool.
Meanwhile, whisk oil, vinegar, mustard, honey, salt and pepper in a small bowl to make dressing.
When the beets are cool enough to handle, slip off the skins. Cut into 1/2-inch cubes and place in a large bowl. Add celery, shallot and the dressing; toss to coat well. Serve at room temperature or chilled.