Heat the sugar, golden syrup and butter in a pan until melted. Mix the ginger and flour in a large bowl and make a well in the centre. Add the bicarbonate of soda to the melted mixture and stir – it will fizz a little – then pour into the flour mixture with the egg. Stir to combine. The mix will be soft but will firm up as it cools.
Scoop the mixture into a box or fridge bag and chill for at least 1 hr until firm enough to roll out. The dough can be kept in the fridge for up to a week or frozen for three months.
Heat oven to 190C/170C fan/gas 5. Turn the dough out onto a lightly floured surface and cut in half. Briefly knead the first piece, then roll it on a lightly floured surface to 2mm thick. Cut into shapes with snowflake or star cutters about 12cm across, then transfer to lined baking sheets, leaving a little room for them to spread. Cut a window out of each biscuit using another cutter about about 6cm across, then add a sweet to the centre.
If the sweets are large, chop them up first – you’ll have to judge by the size of the hole. (Don’t be tempted to add too much or it will spill over the edge.) If you plan to hang the biscuits, make a small hole in the top of each one using the end of a piping nozzle (the hole will close up a little so make sure it’s big enough). Repeat with remaining dough.
Bake in batches for 5-6 mins or until they darken slightly and the sweets have melted. If the holes have closed up, remake them while the biscuits are warm. Leave to cool and harden up completely before moving them. Don’t forget to bake the parts you’ve cut out, too! You can decorate the biscuits further by using white piped icing, if you like.