Prep. time: 15 minutes
Cooking time: 40 minutes

1. Cream together the butter and sugar with a whisk or electric mixer until smooth and light.
2. Preheat the oven to 180° C /350° F.
3. Separate the eggs. Blend the yolks into the butter/sugar mixture, followed by the flour, baking powder and walnuts.
4. Beat the whites with a pinch of salt to form stiff peaks. Fold them gently into the batter.
5. Divide the batter into two parts. Add the cocoa to one part, leaving the other part plain. Pour the two batters alternately into a buttered loaf pan.
6. Bake in the preheated oven for 40 minutes. Cool for 5 minutes before unmolding onto a rack.
7. Dust with icing sugar as desired.