01 - Preheat oven to 350°F. Line baking sheets with parchment paper.
02 - In a large bowl, cream together softened butter and brown sugar until light and fluffy. Incorporate molasses and egg; mix well.
03 - In a separate bowl, whisk together flour, ground ginger, cinnamon, cloves, nutmeg, baking soda, and salt. Gradually add dry mixture to wet ingredients, stirring until dough forms.
04 - Divide dough in half, shape into discs, wrap in plastic wrap, and chill for at least 1 hour.
05 - Roll out chilled dough onto a floured surface to 1/4-inch thickness. Cut out house parts: two walls, two roof panels, and two gable ends. Transfer shapes to prepared baking sheets.
06 - Bake for 12 to 15 minutes until pieces are firm and lightly browned. Cool completely on wire racks.
07 - Beat egg whites and lemon juice until frothy. Slowly add powdered sugar while beating until stiff peaks form.
08 - Transfer royal icing to a piping bag. Pipe icing along edges of gingerbread pieces and press together firmly. Hold in place briefly to set. Allow assembled structure to dry for at least 1 hour.
09 - Use remaining royal icing as adhesive to attach assorted candies. Let icing dry completely before handling.