Preheat your oven to 180°C/Fan 160°C. Place all the cake ingredients into a large bowl and beat until thoroughly blended and smooth.
Divide the mixture between the Mini Loaf Tin and level with a teaspoon. Bake on the middle shelf of your preheated oven for about 20-25 minutes or until well risen, the tops of the cakes spring back when pressed in the centre and a wooden skewer inserted into the middle of the cakes comes out clean. Leave to rest in the tin for a few minutes then ease out onto a wire cooling rack.
For the topping, place all the ingredients, except the walnuts, into a bowl or food processor and blitz until smooth. Spread over the tops of the cakes, swirling the mixture with a spatula if you’d like a more decorative effect, then top with the walnut pieces. Chill a little before serving and store in the fridge.