Geode Cake

Name: Geode Cake
Prep time: 1 h 30 min
Cook time: 4 h
Total time: 4 h
Yield: 24 portions
Ingredients: 500 g caster sugar; 2 Tbsp glucose syrup; 4 drops purple food colouring gel; 2140 g water; 2 tsp vinegar; unsalted butter; 400 g caster sugar; 400 g unsalted butter; ½ tsp fine sea salt; 1 Tbsp vanilla bean paste; 6 medium eggs; 50 g unsweetened cocoa powder; 1 Tbsp baking powder; 350 g plain flour; 450 g mascarpone; 450 g whipping cream; 150 g caster sugar; 25 g cocoa powder, unsweetened; 500 g ripe mangoes; 2 Tbsp chocolate chips; 750 - 1000 g fondant icing; icing sugar; 2 - 3 drops yellow food colouring gel