Hi, I am watching "The Great British Bake off" and there are lines that I don't understand. In a scene, a university archivist is explaining about England's oldest known cook book written by the chief master cooks of King Richard II. He says, "There are also lots of dessert dishes in the book, we're seeing the introduction of sugar which was extremely expensive at the time, and it's a way of demonstrating the luxury that the household could afford." What does this mean? Would someone explain please? Thank you!