pre heat oven to 150c FF, cream room temp butter and icing sugar until pale in colour and light in texture

sift cocoa and plain flour together

add sifted flour mix gradually to butter mix while still mixing slowly to incorporate all flour into butter, use hands to form into a ball of dough,

break off small portions around the size of a small walnut, roll into balls and place on baking tray lined with baking paper, use a fork dipped in icing sugar (shake off excess) to flatten and imprint the biscuits

put the tray of biscuits in the fridge to harden for around 5 minutes, this will stop them from over spreading in the oven

bake for 20 minutes @ 150c FF, remove from oven and cool biscuits on a wire rack

For the filling, mix icing sugar, room temp butter and vanilla together until smooth and lump free once the biscuits are cool sandwich together with icing mix