Beat butter and sugar in a large bowl with an electric mixer until combined. Beat in treacle and egg yolks, then stir in the sifted dry ingredients. Knead dough on a lightly floured surface until smooth, cover; refrigerate for 30 minutes.
Preheat the oven to 160°C/140°C fan forced. Cut cardboard into a 20cm square and 20cm equilateral triangle. Roll one dough portion on a piece of baking paper large enough to cut out one square and one triangle. Cut shapes from dough using cardboard patterns.
Slide shapes, still on baking paper, onto an oven tray. Repeat with remaining dough and cardboard patterns. Cut out a door and window from one triangle; bake door with shapes.
Bake door for about 15 minutes and larger shapes for about 20 minutes or until firm. Stand 10 minutes before transferring to wire racks.
While the gingerbread is still warm, combine the sugar, water and gelatine in a small microwave-safe dish. Microwave on MEDIUM (55%) for about 30 seconds; stir until dissolved. Brush all gingerbread shapes with the Glaze while still warm.
Beat the egg whites in a small bowl with an electric mixer until just frothy, gradually beat in enough sifted icing sugar until the mixture forms stiff peaks, stir in juice. Keep icing covered with plastic on the surface to prevent drying.
Spread a thin layer of icing on the board as a non-slip base. Trim shapes
to form straight edges, if needed. Assemble gingerbread house on the board as pictured, using the icing to secure pieces together. Spoon icing into a piping bag, pipe along all joins as pictured. Position door in place with icing.
Cut the base of the Summer Roll at an angle to represent a chimney. Join chimney to house with icing.
Thin down a small amount of remaining icing with a little water and use this to pipe peaks of icing on the underside of roof to represent snow. Using a small plain tube, pipe outline decorations on window and door.
Decorate the house with sweets, attaching with icing. Dust house all
over with sifted icing sugar.