Prep: 15min | Baking: 1h
250g butter, room temperature
200g caster sugar
6 small-medium eggs, or 5 large ones
1 tsp baking powder
100g dark chocolate couverture
icing sugar, to sprinkle on top
Preheat oven to 180°C. Grease a cake tin.
Combine butter and 150g sugar in a bowl.
Separate egg whites and yolks. Add egg yolks to the butter-sugar mix, interchanging with flour. Add baking powder, and milk.
Whisk egg whites with the remaining 50g sugar until stiff. Fold it into the batter.
Split out half the batter into another bowl.
Melt chocolate and combine it with the batter in one of the bowls.
Spoon both batters into the cake tin and swirl a knife into it so as to get that 'marble' effect.
Bake 1 hour.
Allow to cool before sprinkling with icing sugar using a sieve.