In a large bowl, cream the butter until soft and add the sugar slowly, beating until light. Add the egg yolks and vanilla and beat to blend well. Whisk together the flour/s, baking powder and salt. Alternately blend the dry ingredients and the milk into the butter mixture in three stages, and beat until smooth.

In a separate bowl, beat the egg whites until stiff but not dry. Stir a third of the whites into the cake batter, and then gently fold in the rest.

Place in the oven and bake for about 20-25 minutes until a tester inserted into the center comes out clean. Remove from oven and cool in pan for 5 minutes before turning out onto a rack to cool completely.

Heat cream until just under boiling. Place the chocolate in a bowl and pour over the cream. Let sit for 1 minute, then whisk to blend the chocolate and cream fully; mixture should be smooth. Place in fridge and chill for about an hour. Remove from fridge and, with an electric mixer, beat on high speed until ganache is fluffy and paler in color. Fully frost the cake.