1. Pre heat oven to 190°C/375°F/Gas 5. Grease and base line 33 x 20cm/13" x 8" approx baking tin. A small roasting tin will also do.
2. Melt the butter and chocolate with the water in a saucepan over a low heat, stirring frequently.
3. Sieve the flour and baking powder into a large mixing bowl. Stir in the sugar.
4. Pour the chocolate mixture into the bowl of dry ingredients and beat.
5. Finally, add the the yogurt and eggs and stir until mixture is evenly mixed.
6. Pour into the prepared tin and bake for approx 40-45 minutes until risen and springy to the touch.
7. Remove from oven and leave to cool in tin before turning onto a wire tray. Leave to cool completely.

To Decorate

1. Melt the chocolate with the water in a saucepan over a very low heat, stir in the cream and remove from the heat.
2. Stir in the butter, then pour icing over the cooled cake using a palette knife to spread it evenly over the top of the cake. When icing is set, cut into squares. Enjoy!