Mix milk and vinegar and set aside. Cream butter and sugar then add egg, and vanilla. Beat in milk, flour and baking powder. Pop 1/4 cup scoops of batter on trays and bake until just firm. While they are cooling combine lemon juice, coconut oil and a tbsp of water with enough icing sugar to make a loose icing. Use half to pipe the white sides. Add cocoa then pipe the dark sides.