For the cookies: Whisk together the flour, baking powder and salt in a small bowl. Beat the superfine sugar and butter with an electric mixer on medium speed in a large bowl until light and fluffy, about 5 minutes; beat in the egg, then the vanilla. Add the flour mixture and mix on medium-low speed until completely incorporated. Divide the dough in half, pat into 2 discs about 1/4-inch thick and wrap in plastic wrap. Refrigerate until firm, about 1 hour.
Position oven racks in the top and bottom thirds of the oven and preheat to 350 degrees F. Line 2 baking sheets with parchment paper. Let the dough sit at room temperature for a few minutes to make rolling easier. Roll out 1 disc of dough at a time on a floured work surface to about 1/4-inch thick. Cut out rounds with a 3 1/2-inch cookie cutter and arrange about 1 inch apart on the prepared baking sheets.
Bake, switching and rotating the pans halfway through, until the cookies are golden brown on the bottom, 10 to 12 minutes. Let the cookies cool on the baking sheets until firm enough to transfer to a wire rack; let cool completely.
For the royal icing: Combine the confectioners' sugar and meringue powder in a large bowl. Add 5 tablespoons water and beat with a mixer on medium-high speed until soft glossy peaks form, adding 1 to 2 tablespoons water if necessary, to make a thick but spreadable icing. Beat in the food coloring, a few drops at a time, to make a deep green color (for grass).
For decorating: Spread the icing on the cookies, almost to the edges. Sprinkle the chopped chocolate covered nuts almost to the edge of the green to resemble dirt. Arrange 3 chewy chocolate candies in a triangle on top to resemble logs in a campfire. Fill the space in the center of each with snipped gummy bears to resemble a campfire and embers. Poke a marshmallow on the end of each pretzel stick and stick in the icing to form a tripod that meets in the center. Let the icing harden, about 1 hour.
Right before serving, light the marshmallows on fire and blow it out when they are toasted to your liking.
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