In a large bowl, sift together the flour, spices and baking powder and put aside. In another bowl beat together the margarine and brown sugar till light. Stir in the treacle, egg and vanilla, followed by the sifted dry ingredients to obtain a soft dough. Wrap up in cling film and chill for 4 hours or overnight. When ready, roll out on a floured surface and cut into 2 large Christmas tree shapes and use any extra trimmings to cut out small stars and mini gingerbread men. Place onto 2 baking trays and bake in the oven at 200°C for 30 minutes. Allow to cool down completely. Meanwhile, whip the cream to stiff peaks then fold in the custard, orange zest and alcohol. Place 1 gingerbread tree onto a serving board and using a piping bag fitted with a plain nozzle pipe spots all over using half the cream. Place the 2nd gingerbread tree on top and repeat the process with the remaining cream. Decorate the top with the extra gingerbread cookies dusted with icing sugar, sliced kumquats, chocolate pieces and fresh foliage.