Preheat the oven to 180 C / Gas 4. Grease and line a 20x23x4cm tin.
Gently melt 100g white chocolate with the butter in the microwave or in a bain marie. (I use a microwave, never had a problem!) Set aside to cool slightly.
Separately, beat the eggs and sugar together. Slowly add the melted chocolate/butter and mix.
Sift in the flour and stir gently. Stir in the chopped nuts and chocolate, then pour the mixture into your tin. Scatter the black cherries evenly over the mixture. Press them gently to help them sink. They will sink further when cooking.
Bake for 35 to 40 minutes.
Allow to cool in the tin then slice into 16 squares. Try to avoid scoffing all at once!