Preheat the oven to 200C/400F/Gas 6 (fan 180C).
Melt the butter, sugar and syrup together in a large pan. Sieve the flour, bicarbonate of soda and ground ginger together into a large bowl and make a well in the centre. Pour in the melted butter mixture, stir it in and, when cool enough to handle, knead to a stiff dough.
Divide the mixture into five equally-sized pieces, cut one of these pieces in half (so you have six pieces in total). Roll each piece out on a sheet of greaseproof paper to ¾cm/⅓in thick. Using the templates, cut out the sections for the roof, sides, front and back of the house. Slide onto three baking trays lined with baking parchment.
Using the template as a guide, a ruler and the rim of a cup, cut out the arched windows on the front and sides of the house. Using a star cutter, cut out a star in the front and back of the house. Using a knife, cut out the door on the front and back of the house and place the doors separately on the baking trays.
Re-roll the trimmings and use to cut out the chimney pieces, three Christmas trees and three triangles to use as supports to help the trees stand upright. Bake the gingerbread for 7-8 minutes.
Meanwhile place the boiled sweets in a pestle and mortar and crush to a rough sand texture.
Remove the gingerbread from the oven. Trim the windows if the mixture has spread and sprinkle the crushed sweets into the windows. Return to the oven and continue to cook for 3-4 minutes, or until the sweets have melted and the gingerbread is firm. Remove from the oven and leave to cool for a few minutes, then trim around the templates again to give clean, sharp edges. Leave to cool completely.
For the icing, whisk the egg whites in a large bowl until frothy. Using a wooden spoon or a hand-held electric mixer on slow speed, add the icing sugar a tablespoonful at a time. Stir in the lemon juice and beat the icing until it is very stiff and white and stands up in peaks. Cover the surface with a damp cloth if not using immediately.
Spoon a little of the icing into a piping bag fitted with a medium plain nozzle. Pipe blobs of icing on the back of each chocolate button and stick, overlapping onto the two roof sections, to create a tile effect. Transfer some icing to another piping bag fitted with a small plain nozzle and pipe frames around the windows, doors and stars to decorate. Spoon six tablespoons of the icing over the cake board and, using a palette knife, spread the icing to cover the board with a snow effect and to create a base to stick the house on to.
Pipe some icing along the wall edges and join the house together on the iced cake board. Leave the icing to dry and harden for a minimum of four hours, but preferably overnight.
Once dry, place two night-lights inside the house before attaching the roof.
Cut the pointed ends of the cocktail sticks into 1cm/½in pieces (you should have 12 small pointed pieces). Push the blunt end of the cocktail stick pieces into the sloping edges of the front and back of the house, leaving the pointed ends sticking out to act as peg supports to attach the roof. (Remember to remove the sharp cocktail sticks from your gingerbread house before eating it, to avoid a choking hazard.) Pipe icing between the cocktail sticks and fix the two roof panels onto the house. Pipe icing around the base and edges of the chimney and attach to the roof.
To decorate, pipe icing along the apex and edges of the roof to look like snow and icicles. Stick the front door in place with icing. Cut the back door into three pieces to use as props to keep the trees upright. Decorate the Christmas trees with piped icing and fix them onto the cake board with icing and gingerbread props. Dust the roof with icing sugar and light the night lights using a candle lighter through the open back door. Do not leave the candles lit unattended, and it is best not to burn the candles inside the house for longer than 15 minutes or they may singe the inside of the roof and start to melt the chocolate buttons.