Preparation time: 20 minutes
Cooking time: 50 minutes
For the frosting:
1. Use a 25cm (10in) fluted ring tin. Coat lightly with non-stick cooking spray and dust with flour, tapping out any excess. Preheat the oven to 180°C (gas mark 4).
2. Sift the flour, mixed spice and bicarbonate of soda into a large bowl and make a well in the centre. Whisk the buttermilk, oil, sugar, eggs and 2 teaspoons essence in another bowl until frothy. Pour into the flour mixture and whisk until just combined. Fold in the grated carrots.
3. Pour the batter into your cake tin; smooth the top. Tap the tin lightly on a flat surface a few times to break up any air bubbles. Bake for about 50 minutes, or until a skewer inserted in the centre comes out clean. Cool in the tin for 10 minutes; turn onto a wire rack; flip top-side up; cool completely.
4. In a medium bowl, beat the cream cheese with the remaining vanilla essence and extra buttermilk until softened. Gradually stir in the icing sugar just until frosting is smooth. Place the cake on a serving plate and coat with the frosting, letting some run down the side. Refrigerate the cake until ready to serve.