Preheat oven to 350°Whisk together baking powder, soda, salt, cinnamon and flour. Use a mixer to beat together sugar and butter. Add egg, molasses and ginger, and gradually add in the flour mixture.Cover dough in plastic wrap once combined and refrigerate 1 hour. Line baking sheets with parchment paper and use a 1/2 teaspoon or teaspoon to scoop dough. (I prefer the full teaspoon size). Roll dough into balls and roll in sugar. Chill dough balls on sheets for 15 minutes. Bake for 8-9 minutes once chilled. You will want to make sure you do not over-bake the cookies! They're much better when they're on the soft side. Allow the cookies to set 2 minutes and then carefully transfer to a cooling rack.
Orange buttercream
Using an electric mixer, combine all ingredients and pipe a small amount of frosting in between 2 cookies.