For the apple yogurt cake: Preheat the oven to 180 degrees Celsius. Beat the butter with the sugar in a mixer until light and fluffy. Add the eggs one by one, gradually incorporating them into the mixture.
Add the grated apple, yogurt and cinnamon followed by the flour, baking powder and walnuts. Stir together until well combined.
Butter and flour a cake mould. Pour in the mixture and bake for approximately 1 hour. Ice the cake when cold, or simply dust with a little cinnamon and icing sugar.