Pre-heat the oven to 180ºC/350ºF/Gas Mark 4 and grease and line a 20cm (8 inch) loose bottomed cake tin.
In a large bowl, sieve together the flour, Bicarbonate of Soda, Baking Powder, spices and sugar.
Combine the eggs with the oil and add to the dry ingredient. Beat until smooth.
Add the carrots, sultanas and chopped nuts and mix well.
Pour into the tin and bake for approx. 55 minutes until firm to the touch. Leave to cool in the tin for 10 minutes then transfer to a wire rack.
To make the filling, put the cream cheese and butter into a large bowl and beat until smooth. Add the Vanilla Extract and the milk then gradually beat in the icing sugar.
When the cake has cooled completely, cut in half and sandwich together with half the filling. Spread remaining filling on top.
Add the remaining walnut halves to decorate.