What is a Double Decker chocolate bar made of? A contrasting combination of crispy cereal and soft, pillowy nougat, layered up and coated in smooth Cadbury milk chocolate, giving you two bars in one! Introduced in 1976, the eponymous Cadbury Double Decker chocolate bar derives it's name from the double decker bus. It's a delicious, filling treat - sure to please your sweet tooth (teeth?)