In a large bowl stir together flour, brown sugar, cinnamon, ground ginger, baking powder, baking soda, and allspice. Add shortening, molasses, the water, and egg. Beat with an electric mixer on low to medium speed until combined. Beat on high speed for 2 minutes. Fold in crystallized ginger.
Pour batter into prepared baking dish, spreading evenly. Bake for 35 to 40 minutes or until a toothpick inserted near the center comes out clean. Serve warm with Lemon-Butter Sauce.
In a small saucepan combine sugar and cornstarch. Stir in half-and-half and butter. Cook and stir over medium heat until mixture is bubbly. Reduce heat; cook and stir for 1 minute. Remove from heat. Stir in lemon peel, lemon juice, and ginger. Serve warm.