Melt 50 g/2 oz of the chocolate with the
butter or margarine on High for 2 minutes. Beat in the sugar and eggs,
then stir in the flour, baking powder, vanilla essence and milk until
smooth. Spoon into a greased 20 cm/8 in square microwave dish and
microwave on High for 7 minutes. Leave to cool in the dish for 10
minutes. Melt the remaining chocolate on High for 1 minute, then
spread over the top of the cake and leave to cool. Cut into squares.