Melt the chocolate and butter in a double boiler. Once the chocolate and butter melted set aside and stir nicely with a spatula to make sure the mixture is smooth and lump free.
Sift the flour, baking powder, salt and coffee powder together in a separate bowl.
In the melted chocolate beat in sugar, vanilla, chocolate essence for 3 – 4 minutes at low speed.
Alternatively mix in sifted flour, walnuts and milk until all moistened and combined well. Do not mix the batter for too long.
Preheat the oven to 180 degree celcius. Grease an 8 inch square tin and line with a parchment paper.
Pour the mixture into the prepared tin and bake for 25 minutes.
Remove from the oven and place on a wire rack to cool. Cut into squares and serve hot with vanilla ice cream.