Step 1) Preheat oven to 350°F. Spray a 9-inch square baking pan with nonstick spray.
Step ) For GINGERBREAD CAKE: Mix flour, baking powder, ginger, cinnamon, baking soda and salt in a large bowl. Add molasses, corn syrup, oil and egg; beat until smooth. Beat in water.
Step 3) Pour batter into prepared pan.
Step 4) Bake for 35 to 40 minutes or until toothpick inserted in center comes out clean. Cool.
Step 5) For LEMON SAUCE: Mix sugar and corn starch in small sauce pan. Gradually stir in water.
Step 6) Cook over medium heat, stirring constantly until mixture boils. Boil and stir for 1 minute; remove from heat. Stir in lemon peel, juice, and butter.
Step 7) Serve sauce warm or cool with gingerbread cake. Refrigerate any leftover sauce.