Drain a glass of sour cherries (approx. 350 g drained weight) on a sieve.
Bring 100 g cream to the boil, finely chop 100 g dark chocolate couverture and dissolve. Bring 100 g of cream to the boil, finely chop 100 g of white couverture and dissolve.
Mix the butter, sugar and vanilla until frothy. Sift the flour, cornstarch and baking powder. Stir eggs alternately with flour into the butter mixture at speed 1.
Halve the mixture and stir in the dissolved couverture.