Cream the butter and sugar with an electric mixer until pale and light.
Add vanilla essence and mix well. Add the egg and mix thoroughly.
Sift together the flour, baking powder, Bi-Carb and salt. Gradually add to the creamed mixture to form a dough. Wrap dough in cling film and refrigerate for an hour.
Preheat oven to 170oC. Line three oven trays with baking paper.
Lightly flour the work surface and roll out the dough evenly to a thickness of approximately 5mm. Using cookie cutters, cut out shapes from the dough and arrange on the prepared baking tray.
Bake for 10-12 minutes on the middle shelf. Allow the biscuits to cool completely before decorating.
TO MAKE ICING: Using an electric mixer, whisk egg whites with lemon juice until combined. Gradually add icing sugar on low speed until smooth. For coloured icing, add a few drops of food colouring of your choice.