Melt butter and chocolate. Let cool.
Mix together the melted cooled chocolate mixture, sugar, egg and vanilla until creamy. Add the Flour, soda and cocoa. Cover bowl and refrigerate at least two hours.Preheat oven to 175 C and cover two cookie pans with parchement paper.Make nut sized balls from the chocolate mixture and roll in the powdered sugar till covered completely. Bake in oven approx. 8-12 minutes until cookies just begin to spread.
Remove immedietely and cool completely.