Preheat oven to 400 degrees. Trim the beets and wrap in a foil packet and drizzle with 1 Tablespoon water before sealing. Roast for 1 hour or until tender when pierced with a knife. Once the beets are cool, peel them by rubbing the skins off with a paper towel. Cut the peeled beets into 1 inch pieces and toss with 2 Tablespoons of both the white balsamic vinegar and olive oil and set aside.
In a medium sized bowl, whisk together the remaining white balsamic with the mustard until well combined.