Preheat oven to 160 C. Prepare 8" pan with parchment paper and set aside.

In a medium saucepan melt butter, chocolate, water. Whisking constantly, over low heat for well combined. Remove from heat and let it stand until mixture is at room temperature.

Sift the flour, cocoa powder and bicarbonate of soda together.Whisk sugar,vanilla essence and eggs in a large mixing bowl until pale and creamy. Whisk in the chocolate mixture until well combined.

Add the flour and whisk until combined.

Pour mixture into prepared pan.Bake for 15 to 20 minutes or until a toothpick inserted at the center comes out clean. Remove from oven and let stand in pans for 10 minutes. Then turn out onto wire cooling racks and cool completely.

Chocolate Ganache :Place chocolate pieces in a large bowl.Heat the cream and butter in a small saucepan over medium heat and bring just to a boil. Immediately pour the boiling cream over the chocolate and allow to stand, without stirring, for a few minutes. Then stir gently until smooth.

Now chill the cake.Cover the sides and top of the cake with a thin layer of ganache using a knife.Now refrigerate the cake for about 5 minutes. Later Spread the remaining chocolate ganache evenly over the top and sides of the cake. Set aside for 10 minutes to set.

Decorate the cake with chocolate curls to serve.