Cut off the turnip greens and reserve for making Nameshi (rice with turnip greens). Peel the turnips and reserve the skin for making Kinpira (turnip and carrot salad). Slice across the bottom of each turnip to make a flat base. Carefully use a melon baller or a teaspoon to scoop out the turnip. Mince this and set it aside. Take out one shrimp and coarsely chop. Put the remaining shrimp into a container and puree with a hand blender. Add the egg white and the salt and blend well. Mix in the minced turnip. Coat the inside of the turnip cup with cornstarch. Stuff the turnip and place a pinch of the coarsely chopped shrimp on top. Place the stuffed turnips side-by-side in a pan with a tight-fitting lid. Mix together the dashi, mirin, sake, soy sauce and pour it over the turnips in the pan. Steam the turnips over medium-high heat until tender (about 10–12 minutes). Serve warm.