The cake itself is based around a standard victoria mix (4oz sugar, 4oz butter, cream them together, add 3 eggs one at a time, then fold in 4oz flour. Add milk till a spoon of mix taken from the bowl and held above it takes five seconds to fall back in) with 3oz chopped, blanchedwalnuts added...in fact the best way of getting a walnutty flavour in the cake is to banch the nuts in milk then use this milk in the recipe, or to add a spoon of walnut oil. This mix will fill a medium loaf tin...cook at 160C or so for about 30 mins, or until cooked through. When cold split in 3. The filling is basically buttercream....take some good quality butter, slightly salted is best, then cream in icing sugar, roughly an equal amount but do it to taste. Flavour with vanilla extract.
Alternatively you can split the mix before cooking and cook 3 layers separately.