Preheat oven to 350 degrees. Butter three 8-inch round cake pans and line with parchment. Butter parchment and dust with flour, tapping out excess.
Combine boiling water and baking soda in a medium bowl. Sift flour, baking powder, ground ginger, cinnamon, cloves, nutmeg, and 3/4 teaspoon salt into a large bowl.
Beat butter with a mixer on high speed until pale and fluffy. Add brown sugar and beat until fluffy. Beat in molasses, grated ginger, baking soda mixture, and flour mixture. Beat in eggs.
Divide batter evenly among pans. Bake until a toothpick inserted into center of each comes out with moist crumbs attached, 30 to 35 minutes. Let cakes cool in pans set on wire racks for 15 minutes. Turn out cakes onto racks and let cool completely.
Trim top of each cake using a serrated knife to create a level surface. Transfer 1 cake to a platter. Spread 1 1/4 cups frosting over the top. Top with another cake. Spread 1 1/4 cups frosting over the top. Top with remaining cake. Spread a generous 1/2 cup frosting in a thin layer over top and sides of cake to create a crumb coat. Refrigerate until firm, about 30 minutes. Spread remaining frosting over top and sides of cake using a mini offset spatula to make small swoops on top. Refrigerate for 30 minutes.
Cake layers can be refrigerated, wrapped in plastic wrap, for up to 2 days.
I made this for a Christmas birthday & it was VERY popular.
The creamy mascarpone frosting compliments the spicy cake perfectly and it's not too sweet. The cake is dense and has a bit of a bite due to the 1 tbsp ground ginger & 1.5 tbsp fresh ginger root (but we loved it). Thanks for the great recipe!