- Preheat the oven at 160°C. Grease a cake tin with butter and dust with refined flour. Set aside. 2. Take butter in a large microwave bowl, add chocolate and microwave till the chocolate melts. Allow the mixture to cool to room temperature. 3. Take castor sugar in another large bowl, break in the eggs and add vanilla essence. Beat with an electric beater till the mixture is light and fluffy. 4. Add the chocolate mixture and set aside. 5. Take flour in a bowl and add ½ cup walnuts and mix well. Transfer this into the eggs mixture and fold in and combined lightly. 6. Pour the batter in the prepared cake tin and sprinkle the remaining walnuts on top. Bake for 20-25 minutes. 7. Take the cake tin out of the oven and allow to cool to room temperature and de-mould. Cut into wedges. Sprinkle icing sugar on top