Easter chocolate truffle cake

Name: Easter chocolate truffle cake
Ingredients: 150ml sunflower oil or groundnut oil, plus extra for greasing; 175g self-raising flour plus extra for dusting; 4 tbsp cocoa powder; 1 tsp baking powder; 1 tsp bicarbonate of soda; 140g golden caster sugar; 2 tbsp golden syrup; 2 eggs; 150ml full-fat milk; 125ml double cream; 1 tbsp soft butter; 140g dark chocolate (about 70% cocoa solids); 4 tbsp raspberry jam or apricot jam; 100g milk chocolate broken into chunks; 1 tsp soft butter; 50g digestive biscuits; 2-3 tbsp coloured or chocolate sprinkles