Preheat oven to 350 degrees. Butter two 9-inch round baking pans and dust with flour, tapping out the excess.
In a medium bowl, beat the butter until creamy. Add the maple syrup; continue beating. Add the eggs and beat until combined. In a separate bowl, sift together the flour, baking powder, salt and ginger. Add the flour mixture to butter mixture and beat to combine. Beat in the milk and vanilla until combined. Stir in 3/4 cup walnuts.
Divide batter evenly between the pans. Bake for 23-27 minutes, checking for doneness with toothpick. Cool cakes, then turn them onto a rack. When completely cool, frost with Maple Buttercream frosting (see recipe below) and place one cake on top of the other. Press remaining nuts gently onto sides of cake.