Heat oven to 350°F. In a bowl, combine the flour, baking powder, ginger, and salt. Set aside. Peel, core, and grate the apple. Set aside.
In a medium bowl, cream the butter with a mixer until smooth. Add the maple syrup in a slow stream and continue beating about 2 minutes. Add the eggs, 1 at a time, and increase speed to medium-high. Beat until the batter is smooth and fluffy, about 5 minutes.
Reduce speed to low and gradually beat in the flour mixture, then the milk, until smooth. Stir in the grated apple and walnuts, then pour into a greased 10-inch cake pan. Bake until lightly golden and a skewer inserted comes out clean, 40 to 45 minutes. Cool 10 minutes before removing from the pan. Garnish the cake with the apple chips.