In a large bowl, sift together cocoa, flour, bicarbonade of soda and salt, and set aside.
In a separate bowl, beat butter, brown sugar, white sugar, and spices until the mixture is light and fluffy. Set aside.
Melt the chocolate in a bowl over a pan of hot water.
Add the treacle, egg and melted chocolate to the butter and sugar mixture and beat for about 2 minutes.
Slowly add the dry mixture a spoon at a time and mix until just combined.
Pre-heat the oven to 180 degrees and roll out the dough until it is about ¼ inch thick. Flour the surface and rolling pin if necessary
Use festive cookie cutters to cut out shapes and place on baking paper on a baking sheet
Cook in the oven for 8 minutes and leave on a rack until cool.
Decorate with icing and sprinkles.