Make the cookies: Stir together the flour, baking powder and salt in a medium bowl. Beat the butter, granulated sugar and maple sugar in a stand mixer fitted with the paddle attachment on medium-high speed until light and fluffy, 2 to 3 minutes. Add the egg and extracts and beat until combined. Reduce the mixer speed to medium-low and add the flour mixture in 3 batches until just combined. Transfer the dough to a piece of plastic wrap, flatten into a disk and wrap. Refrigerate until firm, at least 2 hours or up to overnight.

Line 3 baking sheets with parchment paper. Cut the dough in half. Roll out 1 piece of dough on a floured surface until ⅛ inch thick, dusting with more flour as needed. Cut out trees with 2- to 3-inch cookie cutters, dipping the cutters in flour as needed. Repeat with the remaining dough. Gather the scraps, chill, reroll and cut out more cookies. (If the dough becomes too soft, refrigerate 15 to 20 more minutes.) Arrange the cutouts 1 inch apart on the prepared pans. Refrigerate until firm, about 30 minutes.

Position racks in the upper and lower thirds of the oven and preheat to 350 degrees F. Bake, 2 pans at a time, switching the pans halfway through, until the cookies are lightly browned around the edges, 11 to 13 minutes. Let cool 5 minutes on the pans, then transfer to racks to cool completely.

Meanwhile, make the royal icing: Whisk the confectioners’ sugar, meringue powder and salt in a stand mixer fitted with the whisk attachment on low speed. Beat in the water and the extracts on medium-high speed until the icing is thick and bright white, 3 to 4 minutes. (It should fall from a spoon in a slow thick drizzle. If it’s too thick, add more water, 1 teaspoon at a time.)

Divide the icing among 3 shallow bowls (wide enough for dipping the cookies). Add 3 drops of each shade of green food coloring to one bowl, scattering them randomly over the top of the icing. Drag a toothpick or skewer through the colors to make swirls. Holding the edges of the cookie, dip the top side in the icing, then carefully lift it up and shake off the excess icing. Transfer to a rack and repeat with more cookies. When the icing colors get too muddled, move on to the second and third bowls of icing until all of the cookies are dipped. Let dry until the icing has completely hardened, 2 to 4 hours.