Position rack in lower third of oven and preheat to 350 degrees F.
Generously grease the bottom and sides of a ring mold pan and dust generously with flour.
Pour the flour, baking soda, and salt in that order into a triple sifter. Sift onto a sheet of waxed paper and set aside. Crack the egg into a small bowl and whisk just to combine the yolk and the white. Pour the molasses, corn syrup and water into a liquid cup measure and stir to combine. Place the butter in the bowl of a heavy-duty mixer.
With the paddle attachment, cream the butter on medium speed until it clings to the sides of the mixing bowl and has a satiny appearance. Add the sugar and scrape down the sides of the bowl. Continue to cream at medium speed for 2 to 3 minutes or until the mixture is lighter in color and fluffy. Keeping the mixer at a medium speed, add the egg, a tablespoon at a time, to the butter mixture. Continue to cream, stopping the mixer and scraping down the sides of the bowl at least once. After about 1 or 2 minutes, when the mixture is light and fluffy and has increased in volume, remove the beater and bowl from the mixer. Scrape batter off the beater. Stir in the lemon zest and the grated ginger. Using a rubber spatula, stir in a quarter of the flour mixture. Then add 1/3 of the molasses mixture, stirring to blend together. Repeat, alternating dry and liquid ingredients and ending with the flour. Scrape the sides of the bowl often and mix until smooth after each addition.
Pour the batter into the ring mold and spread it slightly higher toward the outer edge so it will bake more evenly. Bake for about 35 to 37 minutes, or until the sides begin to contract from the mold, the surface springs back slightly when lightly touched in the center and a wooden toothpick inserted comes out clean.
Place the cake on a rack to cool for 5 to 10 minutes. With mitts, tilt and rotate the mold and gently tap it on the counter to see if the cake is releasing from the sides of the mold. If not, run a small metal spatula or the blade of a table knife around the outer edge to loosen the cake from the mold. Place an 8 inch wide strip of parchment paper, then a rack on the top of the cake, invert and carefully remove the ring mold. Cool completely.
To make a pattern for decorating the cake, place a cooling rack on top of the cake. Pour the powdered sugar into a sieve and gently sprinkle the sugar evenly over the cake. Remove the top cooling rack and transfer cake to a serving platter.