Preheat oven to 350 degrees.
Grease and lightly flour two 9x2-inch round cake pans, then line the bottoms with waxed paper.
To make the cake: In a large bowl, sift together the flour and the ginger and set aside.
In a large bowl, cream the butter and the sugar until fluffy, about 3 minutes. Add the eggs one at a time, beating until well combined. Beat in the maple syrup gradually. Add the flour mixture in thirds, alternating with the water, beating after each addition until smooth. Divide the batter between the prepared pans and bake for 30-35 minutes or until a cake tester inserted into center of cake comes out clean.
Let cakes cool in pans for 10 minutes. Remove from pans and cool completely on wire rack.
To make the frosting: In the top of a double boiler, combine first five ingredients. Cook over boiling water, beating constantly on the medium-high speed of an electric mixer, until mixture stands in peaks (about 5-7 minutes). Remove the pot from heat. Add the vanilla and the maple extracts and continue beating 1 minute more until thick enough to spread.
When cake has cooled, ice between the layers. Sprinkle about 1/3 cup chopped walnuts over the frosting. Then ice top and sides of cake, sprinkling the top with the remaining chopped walnuts.
The Magnolia Bakery Cookbook, Simon & Schuster