Melt Ingredients: In a saucepan, heat unsalted butter and golden syrup, stirring until bubbling. Remove from heat, add chopped chocolates, and mix until smooth.
Combine Mixtures: Pour the melted chocolate mixture over the dry ingredients and fold gently until everything is evenly coated.
Set Pudding: Transfer the mixture into the prepared bowl, press down firmly, cover, and refrigerate for at least 2 hours.
Decorate: Remove from fridge, invert onto a plate, drizzle with melted white chocolate, pipe buttercream decorations, and add red M&Ms.