Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan.
In a medium bowl, sift together the flour, cocoa powder, baking powder, baking soda and salt. Set aside.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the buttermilk, water, and vanilla. Beat in the flour mixture until just blended. Fold in the dark chocolate chips.
Pour batter into the prepared pan. Bake for 30 to 35 minutes in the preheated oven, or until a toothpick inserted into the center of the cake comes out clean.
To make the frosting, melt the dark chocolate chips and heavy cream together in a double boiler. Once melted and smooth, allow to cool slightly before spreading over the cake.
Interesting Facts
Dark chocolate contains flavonoids, which are natural compounds that may lower blood pressure and improve cholesterol levels.