Preheat oven to 180 degrees C. Grease a 20cm round cake tin.
Beat together the butter and sugar. Add the egg yolks one at a time, beating in between. In a separate bowl, beat together the egg whites and salt until they form stiff peaks then set aside.
Stir together the chocolate, vanilla and the pecans then add it to the butter mixture along with the flour. Fold in the egg whites then pour into the prepared cake tin.
Bake in the preheated oven until a knife inserted into the centre of the cake comes out clean, about 50 minutes. Allow to cool in tin for 10 minutes before moving to a wire rack. Dust with icing sugar and serve warm.