1. Place the chocolate sponge mix and drained mandarin orange segments in a bowl fitted with a whisk. Blend in the drained juice on slow speed for 1 minute, scrape down and then mix for a further 4 minutes on medium speed.
2. Transfer to a greased tin.
3. Bake in a preheated oven at 190C / 375F / Gas Mark 5 for 20-25 minutes until risen and firm to touch.
4. If serving cold, allow to cool before cutting in to portions.