Preheat the oven to 180°C, 160°C fan oven, Gas mark 4.
Cream the Stork, sugar and coffee essence until light and fluffy.
Add the eggs one at a time and beat well.
Fold in the flour, cocoa and baking powder using a metal spoon.
Place in a greased 28 x 18cm (11 x 7 inch) Swiss roll tin and spread evenly.
Bake in middle of the preheated oven for 25 - 30 minutes. Turn out and cool on a wire tray.
To make the topping, melt the chocolate in a bowl over hot water. Add the milk and Stork and beat until smooth and glossy.
Stir in the coffee essence.
Spread over the brownies and cut into squares.
Decorate with walnuts.
Recipe courtesy of Stork