Giant jaffa orange cake

Name: Giant jaffa orange cake
Ingredients: 250g pack butter softened, plus extra for greasing; 300g golden caster sugar; 4 large eggs; 100g full-fat natural yogurt; 300g plain flour; 2 tsp baking powder; zest 4 large orange (use the oranges below); juice 5 large oranges (about 500ml), save the zest of 1 orange to finish; 100g golden caster sugar; 6 gelatine leaves; 300ml pot double cream; 200g milk chocolate finely chopped; 100g dark chocolate finely chopped; 2 tbsp apricot jam; zest 1 orange