Autumn carrot cake with prunes and walnuts

4 eggs, separated plus 1 whole egg

100g (3 ½ oz) caster sugar

200g (7oz) light brown sugar

125g (4 ½ oz) unsalted butter, softened

120g (scant 4 ½ oz) oil

2 tsp vanilla extract

500g (18oz) grated carrots (700g/1 ½ lbs before peeling)

150g (5oz) walnuts, lightly toasted and coarsely chopped

150g (5oz) Armagnac-soaked prunes, turn into quarters

zest of 1 orange

315g (10 ½ oz) plain flour

2 tsp baking powder

½ tsp bicarbonate soda

1 tsp cinnamon

1 tsp salt

1 tsp Ras el Hanout

For the frosting:

375g (13oz) unsalted butter, softened

600g (1 ¼ lbs) cream cheese, brought to room temperature

1 tsp vanilla

200g (7oz) icing sugar

1 tbsp lemon juice

2 walnuts for decoration (untoasted)