Heat the oven to 180C/fan160C/gas 4. Oil and line the base and sides of an 18cm square cake tin with baking parchment.
Tip 175g light muscovado sugar, 175ml sunflower oil and 3 large beaten eggs into a big mixing bowl. Lightly mix with a wooden spoon. Stir in 140g grated carrots, 100g raisins and grated zest of 1 large orange.
Sift 175g self-raising flour, 1 tsp bicarbonate of soda, 1 tsp ground cinnamon and ½ tsp grated nutmeg into the bowl. Mix everything together, the mixture will be soft and almost runny.
Pour the mixture into the prepared tin and bake for 40-45 mins or until it feels firm and springy when you press it in the centre.
Cool in the tin for 5 mins, then turn it out, peel off the paper and cool on a wire rack. (You can freeze the cake at this point if you want to serve it at a later date.)
Beat 175g icing sugar and 1½ - 2 tbsp orange juice in a small bowl until smooth – you want the icing about as runny as single cream.
Put the cake on a serving plate and boldly drizzle the icing back and forth in diagonal lines over the top, letting it drip down the sides.
