Adjust the oven rack to the middle position. Preheat the oven to 180°C. Generously butter a 26 cm round ring form cake tin.
Beat eggs, oil and melted butter for 1 minute on high speed until well blended.
Add lukewarm buttermilk and beat briefly on high speed.
Add the contents of the pack and gently mix in by hand with a spatula. Mix only until combined. It is important not to overmix. The mixture will be fairly soft and runny. Scrape mixture into prepared pan. Shake to level.
Bake for 30 minutes. Cake is done when a thin bladed knife inserted in the thickest section comes out clean or the cake pulls away slightly from the sides of the pan.
Cool cake in the pan for 10 minutes. Turn out on a cooling rack. When cake is completely cool, dust with icing sugar before serving with coffee.
The cake improves with standing. Can happily be baked the day before. Keep in an airtight cake tin.