3 cups all-purpose flour, plus more for dusting and rolling (see Cook's Note)
3 tablespoons ground ginger
1 tablespoon ground cinnamon
1 tablespoon freshly ground black pepper
1 teaspoon fine salt
3/4 teaspoon baking soda
1/2 teaspoon ground allspice
1/2 teaspoon freshly grated nutmeg
1/4 teaspoon cayenne
1/4 teaspoon baking powder
1 stick (1/2 cup) unsalted butter cut into 1-inch pieces, at room temperature
3/4 cup granulated sugar
1/2 cup molasses
1 large egg
2 cups confectioners' sugar
1/4 cup meringue powder (egg white powder)
Cinnamon candies, such as Red Hots, chocolate chips, raisins or other candies for decorating
Whisk together the flour, ginger, cinnamon, black pepper, salt, baking soda, allspice, nutmeg, cayenne, and baking powder in a medium bowl.
Beat the butter and granulated sugar in a large bowl with an electric mixer on medium speed until pale and fluffy, about 3 minutes (scrape down the sides of the bowl, as needed). Beat in the molasses until combined, then the egg (the mixture will look curdled). Add the flour mixture and beat on low speed until the dough comes together. Divide the dough in 2 pieces, flatten each half into a disk and wrap each disk in plastic wrap. Refrigerate at least 2 hours or up to overnight.
Position 2 racks in the top and bottom thirds of the oven and preheat to 350 degrees F. Line 2 baking sheets with parchment paper.
Keeping one disk refrigerated, roll the other disk on a well-floured work surface to 1/4 inch thick, sprinkling flour on and under the dough as needed and sliding a spatula underneath every so often to prevent sticking (If the dough looks crackly or breaks apart, press it back together from the outside edge in). Using cookie cutters, cut out gingerbread shapes as close together as possible. Pull away the extra dough around each shape then use a small offset spatula to transfer the shapes to the prepared cookie sheets, spacing them 1 inch apart. Reroll the scraps and cut out more cookies. Freeze the cookies until firm, about 15 minutes.
Bake the cookies, rotating the baking sheets from top to bottom and from front to back halfway through cooking, until they are slightly firm to the touch but not browned at the edges, about 12 minutes. Repeat the rolling, cutting and baking with the remaining dough disk.
Cool the cookies for 5 minutes on the baking sheet then transfer them to a cooling rack to cool completely, about 20 minutes (The cookies will continue to firm as they cool).
Make the icing: Combine the confectioners' sugar, meringue powder and 3 tablespoons water in a large bowl and beat with an electric mixer on low speed until the frosting thickens, trying not to incorporate too much air. (The icing should be pure white and thick, but not fluffy and bubbly.)
Scrape the icing into a resealable plastic bag and snip the corner to the desired size. Pipe the icing onto the cookies to decorate, as desired, sticking the candy onto the icing while it is still wet. Let the cookies stand at room temperature until the icing hardens, at least 1 hour.