Step 1: In a large bowl, cream together the softened unsalted butter and granulated sugar with an electric mixer until light and fluffy, about 2-3 minutes.
Step 2: Beat in the molasses and egg until well combined and smooth.
Step 3: In a separate bowl, whisk together the all-purpose flour, baking soda, ground ginger, ground cinnamon, ground cloves, and salt.
Step 4: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Do not overmix. The dough will be thick.
Step 5: Divide the dough into two equal portions, flatten each into a disk, wrap tightly in plastic wrap, and refrigerate for at least 2 hours, or preferably overnight.
Step 6: Preheat your oven to 350°F (175°C). Line several baking sheets with parchment paper.
Step 7: On a lightly floured surface or between two sheets of parchment paper, roll out one disk of chilled dough to an even 1/4-inch thickness.
Step 8: Using gingerbread house templates (printables can be found online or create your own!), carefully cut out the wall, roof, and other desired pieces. Re-roll scraps gently, chilling if warm.
Step 9: Carefully transfer the cut gingerbread pieces to the prepared baking sheets, leaving a little space between each.
Step 10: Bake for 12-15 minutes, or until the edges are firm and lightly browned. Watch carefully for burning.
Step 11: Immediately after removing from the oven, if any pieces have spread, use your templates and a sharp knife to re-trim the edges while the gingerbread is still warm.
Step 12: Let the gingerbread pieces cool completely on the baking sheets for 10 minutes before carefully transferring them to a wire rack to finish cooling. They must be completely cool and firm before assembly.
Step 13: For the royal icing: In a large bowl, combine the meringue powder and warm water. Beat with an electric mixer on high speed for 5-7 minutes until stiff peaks form.
Step 14: Gradually add the powdered sugar, one cup at a time, beating until smooth after each addition. Continue beating on high for another 2-3 minutes until the icing is very thick and holds stiff peaks. Keep covered.
Step 15: To assemble, pipe a generous line of royal icing along the bottom and side edges of your first wall piece. Firmly press it onto your serving platter or base. Prop with cans or jars if needed.
Step 16: Continue with the remaining walls, ensuring connections are firm. Allow the walls to dry for at least 1-2 hours, or preferably overnight, before adding the roof.
Step 17: Once walls are secure, pipe generous lines of royal icing along the top edges of the walls and the connecting ridge for the roof. Carefully place roof pieces on top, holding until stable. Let the entire structure dry completely, ideally overnight, before decorating.
Step 18: Decorate your gingerbread house with candies, sprinkles, and additional royal icing for snow and details. Let your creativity shine!
Step 19: Store your finished gingerbread house in a cool, dry place. It can last for several weeks.