Birthday cake trifle

Name: Birthday cake trifle
Cuisine: European, British
Ingredients: 14 oranges juiced (to make 750ml juice), strained through a fine sieve, plus zest of 1 orange; 1/2 cup (110g) caster sugar; 4 titanium-strength gelatine leaves, soaked in cold water for 5 minutes to soften; 1 mandarin, segmented; 300ml thickened cream; 100g sour cream; 1/3 cup (40g) pure icing sugar, sifted; 300g store-bought chocolate caramel brownie, torn into large pieces; Grand Marnier, to drizzle; 1/3 cup (45g) toasted slivered almonds; Sprinkles, to serve; 500g dark (70%) chocolate, finely chopped; 2 cups (500ml) pure cream; 400g dark (70%) chocolate, finely chopped; 200g each white & milk chocolate, finely chopped; 4 eggwhites; 1 cup (250ml) thickened cream; 1 tsp vanilla extract; 200g milk chocolate, finely chopped; 80g Coco Pops