Start cooking about 8h before baking and serve the earliest 1-2 hours after baking.
8-10 slices
Mix the orange juice and zest with the sultanas and leave overnight or heat and leave to cool. Line a 2 lb. loaf tin with baking paper.
Heat the oven at 180 degrees.
Mix all the dry ingredients together, then add the remaining ingredients and mix until combined.
Tip into the prepared tin and bake for about 1 hour then cool in tin.
Once cool, make the icing by mixing all icing ingredients carefully so the mascarpone doesn’t curdle.
If eating all cake the same day, spread on top of the cake and decorate with the walnut halves. If not eating all the same day, keep the cake un-iced in a closed tin at room temperature and keep the icing in the fridge. When eating, spread some of the icing on the cake slices.