- Peel the apples and cut into small cubes. Season with the lemon juice and its zest, stir and set apart.
- Beat the butter with sugar until creamy and soft. Add the eggs, one at a time and keep on whipping at low speed.
- Sift the flour and the baking powder, and gradually add to the butter mixture. Stir in the apples and the walnuts.
- Spread into a 22cm diameter baking tray lined with parchment paper and bake 180 degrees for about 30 minutes.