100g walnuts or pecans, roughly chopped (optional)
For the icing
100g slightly salted butter, softened
300g icing sugar
100g soft cheese
Heat oven to 180C / 160C fan / gas 4. Oil and line the base and sides of two 20 cm cake tins with parchment paper. Whisk the oil, yogurt, eggs, vanilla and zest in a jug. Combine the flour, sugar, cinnamon and nutmeg with a good pinch of salt in a bowl. Squeeze the lumps of sugar between your fingers, shaking the bowl several times to bring the lumps to the surface.
Add the wet ingredients to the dry, along with the carrots, raisins and half the nuts, if using. Mix well to combine, then divide among the tins.
Bake for 25 to 30 minutes or until a skewer inserted in the center of the cake comes out clean. If a wet mixture sticks to the skewer, return to the oven for 5 minutes, then check again. Leave to cool in the tins.
To make the frosting, beat butter and sugar together until smooth. Add half of the soft cheese and beat again, then add the rest (adding little by little prevents the icing from cracking). Remove cakes from tins and sandwich with half of the icing. Top with remaining icing and sprinkle with remaining nuts. Keeps in the refrigerator for up to five days. Best consumed at room temperature.