125g (4.4 oz, about 2-3 carrots) of peeled and grated carrots
For the icing
340g (12oz) mascarpone cheese, room temperature
3/4 cup (about 100g) icing (confectioners') sugar, sifted
1 tbsp powdered ginger, can be adjusted to taste
Zest of 1 lemon + 2 tsp lemon juice
1 1/2 cups (about 360ml) thickened (heavy) cream
For the cake
Grease well and line the base and sides of three 18cm (7inch) round cake tins, or two 20cm (8inch) tins. Preheat oven to 200°C (390°F) (or 180°C (350°F) fan-forced). Place the walnuts on a baking tray and cook for 4-5 minutes or until lightly roasted. Cool and cut into thirds. Sift the flour, baking powder, baking soda, cinnamon, cloves, nutmeg and salt into a bowl. Repeat to ensure they are evenly mixed. Put the egg whites in a large clean bowl. Whisk egg whites on high speed with an electric mixer until soft peaks start to form. Slowly add 60g of sugar while whisking and continue mixing until soft peaks form. Transfer the meringue to another bowl and set aside until needed.
Place the egg and egg yolk in the large mixing bowl and add the sugar for egg yolks. Mix on high speed with an electric mixer for 3-4 minutes or until the mixture doubles in volume and is quite airy. With the mixer still on, slowly pour the oil in a thin stream being careful that it doesn’t split or deflate too much. Remove the bowl from the mixer and with a spatula, gently fold in the flour mixture until combined. Fold in the carrots and walnuts. Working quickly, lightly fold in the meringue, but do not fold in completely. You should still be able to see some white streaks through the mixture. Pour equal amounts of the mixture into the prepared tins and bake for 25-30 mins, or until a skewer inserted into the centre of the cake comes out clean and the surface of the cake springs back when lightly pressed. If using two or one tin instead of three you should increase your baking time accordingly. Cool in tin for 5 minutes then carefully remove and cool completely on a wire rack.
For the icing
Place mascarpone, icing sugar, powdered ginger and lemon zest and juice in a large mixing bowl and whisk together with a hand whisk until smooth. In a separate clean mixing bowl, whisk cream until soft peaks form. Take care not to overwhip. Fold cream into mascarpone mixture until smooth then place in a piping bag with a 1cm round tip.
Place one layer of cake on your cake stand or plate. Pipe rounds of icing just inside the edge of the top of the cake if you want to create the scalloped effect, then fill in the rest of the top of the cake. Cover with another layer of cake and repeat. For the top of the cake I spread a thin layer of icing using a spatula and then repeated the piped rounds around the edge of the cake and topped with soft silver cachous and a dusting of icing sugar. Alternatively you can just dust with icing sugar or top with a smooth layer of icing and more toasted walnuts. Keep chilled in the fridge until ready to serve.