In a stand mixer fitted with a paddle attachment, or using a hand mixer, beat the butter, brown sugar, and maple syrup together until light and fluffy. Add the egg, grated ginger, and lemon zest. Mix until well combined.
1 cup unsalted butter, 1 cup packed light brown sugar, 1 cup pure maple syrup, 1 large egg, 2 tablespoons fresh ginger, 2 teaspoons lemon zest
In a separate bowl, sift together the flour, ground allspice, ground cinnamon, baking soda, and salt.
4 ⅔ cups all-purpose flour, 1 teaspoon ground allspice, 1 teaspoon ground cinnamon, 1 teaspoon baking soda, 1 teaspoon salt
Gradually add the dry ingredients to the butter mixture in three parts, mixing on low speed until a smooth dough forms. The dough will be soft. Divide the dough into two portions. Wrap each in plastic wrap, flatten into discs, and chill for about 2 hours, or until firm.
Preheat the oven to 350F (180C).
Remove one disc of dough from the refrigerator and roll it out between two sheets of parchment paper to about one-fourth inch thick. Thicker pieces will make the house sturdier.
Lightly flour the underside of your gingerbread house cookie cutters, then cut out the house shapes—two of each piece. Use any leftover dough to make fun shapes with smaller cookie cutters.
Carefully transfer the cut pieces to baking sheets lined with parchment paper, spacing them about three inches apart. If any shapes get distorted, gently reshape the edges.
Bake the larger house pieces for 18 to 20 minutes, or until the edges are lightly browned. Bake smaller pieces, like chimneys, for 12 to 13 minutes. Let all pieces cool completely on the baking sheets before assembling.
In a clean mixing bowl, beat the egg whites on high speed until thick, white, and fluffy—about 5 minutes. Add the sifted icing sugar and lemon juice. Mix on low speed until smooth and combined.
4 egg whites, 4 cups icing sugar, 2 teaspoons lemon juice
Keep the icing covered to prevent it from drying out. Store it in a piping bag or sealed container at room temperature (do not refrigerate).
Assemble the house by applying royal icing along the edges of each piece to “glue” them together. Start with the front, sides, and back, then finish with the roof. If any edges do not align perfectly, trim them carefully with a sharp knife.
Once the structure is set, decorate your gingerbread house with powdered sugar, colorful sprinkles, candies, or any decorations you like.