01 - Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper.
02 - Whisk together flour, ginger, cinnamon, cloves, nutmeg, baking soda, and salt in a large bowl.
03 - Beat unsalted butter and packed brown sugar until light and fluffy. Incorporate molasses and the egg, mixing well.
04 - Gradually add dry ingredients to wet mixture, stirring until combined. Shape dough into a disc, wrap in plastic wrap, and chill for at least 30 minutes.
05 - Roll dough on a lightly floured surface to 1/4-inch (6 mm) thickness. Cut out gingerbread house panels using templates; re-roll scraps as necessary.
06 - Arrange shapes on baking sheets with space between each. Bake for 12 to 15 minutes until firm and edges darken lightly. Cool completely on a wire rack.
07 - Beat egg whites with lemon juice until frothy. Gradually add powdered sugar and continue beating on high until stiff, glossy peaks form (about 5 minutes).
08 - Transfer icing into a piping bag or zip-top bag with a small corner cut. Pipe icing along edges of panels to join, holding pieces together until set. Let assembled house stand 30 to 60 minutes to firm.
09 - Decorate with assorted candies and additional icing as desired. Allow decorations to set before display or serving.