In a large pan, gently melt the butter, brown sugar, and golden syrup together over low heat until smooth. Let this cool slightly, then stir in the beaten egg. Sift in the flour, spices, bicarbonate of soda, and salt, and mix until a firm dough forms.
Wrap the dough and chill it in the fridge for at least 30 minutes, since warm dough spreads too much in the oven. Once firm, roll it out on a floured surface to about 5mm thick for sturdy, stackable walls.
Lay your templates over the rolled dough and cut around them with a sharp knife, then transfer the pieces to lined baking sheets. Bake at 180°C (350°F) for 12 to 15 minutes, until firm and lightly golden at the edges.
Let the gingerbread pieces sit on the baking sheet for five minutes, then move them to a wire rack to cool fully. This step matters more than it seems, since warm gingerbread bends and breaks during assembly.
Whisk the egg whites until frothy, then gradually beat in the sifted icing sugar until you get a thick, glossy icing that holds stiff peaks. Divide and tint portions black and orange for decorating.
Pipe a thick line of white icing along the edges of your wall pieces and press them together, using cans or mugs to prop them upright while they set. Once the walls are firm, attach the roof panels the same way.
Once your structure is fully set, pipe on spooky windows, doors, and cobweb details using your tinted icing. Add sweets for chimneys, tombstones, or creepy little extras, then let everything harden before serving.