Ingredients:
125g unsalted butter, softened
100g light brown sugar
100g granulated sugar
1 tsp vanilla extract
2 large egg whites
110g dark cocoa powder
110g plain flour
1/4 tsp salt
caster sugar for dusting
Method:
Cream together the butter, sugar and vanilla in a bowl until soft and fluffy then add the egg whites, one at a time, beating well after each addition. Meanwhile, sift together the cocoa powder, flour and salt into a bowl then add to the egg and butter mix, beating well to combine.
Scrape the dough onto a sheet of clingfilm then cover with a second sheet of clingfilm and press into a rough disk. Transfer to the refrigerator and chill over night, or until firm. The following day, divide the dough into 3 equal portions then place on a lightly-floured work surface and roll out into a square about 15cm per side. Use a 5cm pastry cutter to cut the dough into rounds and transfer these to lightly-greased baking tray. Prick the rounds all over with a fork (this stops them curling) then dust with a little extra sugar.
Place in an oven pre-heated to 180°C and bake for about 20 minutes, or until they are slightly puffed and firm to the tough. Remove from the oven and allow to cool for 10 minutes on the baking tray then transfer to a wire rack to cool completely.
To store, keep in an air-tight tin.
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