Freaky finger red velvet cake

Name: Freaky finger red velvet cake
Ingredients: 175g soft butter, plus extra for greasing; 225g white caster sugar; 1 tsp vanilla extract; 3 large eggs, at room temperature; 1 tbsp red food colouring paste (we used Christmas red from Sugarflair); 200g plain flour; 50g cocoa powder (we used Green & Black's); 1 ½ tsp bicarbonate of soda; ½ tsp baking powder; ¼ tsp salt; 150g pot low-fat plain yogurt, loosened with 2 tbsp milk; about 3 x 114g boxes white chocolate fingers (we found them in Tesco); 140g icing sugar; 2 tsp milk; small blob of red food colouring paste; 100g soft butter; 300g full-fat cream cheese, fridge cold (we used Philadelphia as it has the firmest texture); zest 1 orange (optional)