Preheat the oven to 175 C degrees. Grease and line a springform cake tin.
Mix the flour, sugar, baking soda, ground cinnamon, mixed spice and pinch of salt together in a bowl.
Peel the mandarins and put one aside. Put the rest (including the rind) into a food processor and whiz until you get a thick puree. Add the shredded carrot and pulse for a few seconds. Add the eggs and pulse for a few seconds again. Finally mix in the oil and vanilla extract.
Pour the wet mixture into the flour mixture and stir gently until you get a smooth batter.
Tip the batter into the prepared cake tin. Arrange the mandarin slices on top and scatter 2 tbsp of muscovado sugar all over the top.
Bake in the middle of the oven for 40-45 minutes until golden and a toothpick inserted into the centre of the cake comes out clean. After 20 minutes or so have a look, if the top is already brown, cover the tin with foil.
Let the cake cool in the tin for 10 minutes, then carefully remove the springform.
Transfer the cake to a wire-rack and allow to cool completely.