Sift the flour, salt and baking powder together into a medium sized bowl
In another medium sized bowl beat the butter and caster sugar together until pale, light and fluffy
Add the egg to the butter and beat until combined
Add the flour mixture slowly to the butter mixture until completely combined
Turn out onto a work surface and knead until smooth
Roll out into two large rectangles and place in the freezer for at least half an hour
Preheat the oven to 180C/ 360F
Cut out the two sheets of rolled out dough into champagne flute shapes (I used a piece of cardboard create a template, and cut around that to make the cookies, makes approx 30 flutes)
In the centre of 10 flutes cut out a rectangle of dough (this is where you will store the sprinkles for the pinata effect)
Place flutes onto a baking tray lined with baking paper and bake for 10 minutes, or until lightly golden brown
Royal Icing
Place the egg whites in a stainless-steel bowl over a small pot of boiling water on the stove
Whisk the egg whites until warm and remove
Whisk in the 2 cups of icing sugar, a spoonful at a time until well combined
Take out half of the icing and put it to the side
Add tan food colouring to one half until desired colour is reached (for champagne)
Into the other half add the extra ¼ cup of icing sugar and mix well (for the glass and glue), it should be a thick but pipe-able consistency- if not add more icing sugar or water to adjust the consistency
Assembly
Lay the cookie with a rectangle cut out on top of a whole cookie
Glue the two together with some white royal icing by piping a border of icing along the edges of the bottom cookie
Fill with your choice of sprinkles until just full
Pipe a line of royal icing along the border of the cookie with the rectangle cut out and place another full cookie on top to seal in the sprinkles
While not moving them from their places pipe the outline of the champagne flutes onto the tops of the cookies
Allow the cookies to dry for 2 hours
Finish decorating by "filling" the glasses with tan royal icing, topping with white royal icing to resemble foam, and piping a few small dots of white to resemble bubbles
Allow to full dry fully for 6-8 hours before packaging! (if you have some lustre dust you can brush that on too!)