How to Make It
Prepare the Cookies: Beat butter and sugar with a heavy-duty stand mixer fitted with paddle attachment on medium speed until light and fluffy, about 2 minutes. Add egg, vanilla, and, if desired, almond extract, and beat until fully incorporated. Gradually add flour and salt to butter mixture, and beat until combined. Remove dough from bowl, and shape into a flat disk. Cover with plastic wrap, and refrigerate at least 2 hours or up to 24 hours.
Preheat oven to 350°F, and line 2 baking sheets with parchment paper. Transfer dough to a lightly floured surface, and roll dough to a 1/8-inch thickness. Cut into desired shapes, and transfer to prepared baking sheets, leaving 2 inches between each cookie.
Bake in preheated oven until cookies are slightly golden on edges but pale in the center, 6 to 10 minutes, depending on the size of cookie. Do not over-bake. Let cool on baking sheets 5 minutes. Transfer to a wire rack, and cool completely, about 30 minutes.
Prepare the Royal Icing: Combine powdered sugar, water, and meringue powder in bowl of stand mixer fitted with whisk attachment. Beat on medium speed until fully combined and smooth, about 1 minute, stopping to scrape sides of bowl as needed. Increase speed to high, and beat until icing is no longer glossy, about 1 more minute. Divide into desired number of portions, and place each portion in a small bowl; tint with desired food coloring.
Place icing in a piping bag or a ziplock bag with 1 corner snipped, and decorate cookies. (To flood top of cookie with icing, thin icing by stirring in 1 tablespoon water at a time until spreadable consistency is reached. Pipe thinned icing onto cookie, and use a wooden pick to spread icing to edges and corners of cookie.)