Butter and line a 30cm x 21cm tin. Preheat
the oven to fan 160/conventional 180/gas 4.
Break up the chocolate with the butter and
melt in the microwave on Medium for about
5 minutes, stirring halfway through.
Beat the sugar and eggs in a bowl. Stir in
the melted chocolate, add the flour and beat
well. Pour into the tin and bake for 40-45
minutes, or until the top looks papery and
feels slightly wobbly. Leave to cool in the tin.
Break up the chocolate with the butter
and melt in the microwave on Medium for
about 1 minute. Stir until smooth then
spread over the cake. Dust with icing sugar
and cut into squares.