Cream the butter and sugar together in a large bowl. Add the beaten egg, food colouring, and the vanilla extract and stir in. Sift the self-raising flour and strawberry powder into the bowl and mix together thoroughly.
Spread onto some cling film and wrap tightly into a cylinder, inside a sheet of silver foil. Chill for at least two hours in the refrigerator.
Preheat your oven to 375 F / 190 C / Gas Mark 5 and line two baking sheets with non-stick baking paper or silicon baking mats. Unwrap the cookie mix and slice into rounds into half a centimetre or the thickness of a pound coin. Space out on to the trays and place into the oven.
Bake for around eight minutes, until they are firm on the edges and just slightly soft in the very centre if you press them. If you prefer a slightly firmer cookie leave in the oven for a couple of extra minutes.
Remove from the oven and leave on the tray for a couple of minutes to set. Carefully cut in half and then lift onto a cooling rack. When cool sandwich two halves together with butter icing and fix in the marshmallow teeth.