3 cups all-purpose flour
1 teaspoon baking soda
3/4 teaspoon ground cinnamon
3/4 teaspoon ground ginger
1/2 teaspoon ground allspice
1/2 teaspoon ground cloves
1/2 teaspoon salt
8 tablespoons (1 stick) unsalted butter, at room temperature
1/4 cup vegetable shortening, at room temperature
1/2 cup packed light brown sugar
2/3 cup unsulfured molasses
1 large egg
Sift the flour, baking soda, cinnamon, ginger, allspice, cloves, and salt through a wire sieve into a medium bowl. Set aside.
In a large bowl, using a hand-held electric mixer at high speed, beat the butter and vegetable shortening until well-combined, about 1 minute. Add the brown sugar and beat until the mixture is light in texture and color, about 2 minutes. Beat in the molasses and egg. Using a wooden spoon, gradually mix in the flour mixture to make a stiff dough. Divide the dough into two thick disks and wrap each disk in plastic wrap. Refrigerate until chilled, about 3 hours.
On a large piece of wax paper, roll out the dough to a quarter-inch thickness. Lightly dust the dough with flour to keep it from sticking to your rolling pin. Use gingerbread templates as guides to cut the dough into parts. After cutting gingerbread house pieces, collect all of the scrape pieces of dough and bake on a flat cookie tray for 15 minutes +- at 350 degrees.
2 pounds confectioners' sugar, sifted
1/2 cup plus 2 tablespoons meringue powder
Scant 1 cup water, plus more if needed
With an electric mixer on low speed, beat ingredients until fluffy, 7 to 8 minutes. Use immediately, or transfer to an airtight container (royal icing hardens quickly when exposed to air) and refrigerate up to 1 week. Stir well with a flexible spatula before using.