What does Mandy discover about the mushrooms Sir Peter wants to serve when a suitor comes to see Ella?

When a suitor comes to see Ella, Sir Peter orders special elvish mushrooms as a delicacy to serve. Mandy finds that the mushrooms contain a love spell which Sir Peter apparently wants to use to trick Ella and her suitor into getting betrothed. Mandy switches the mushrooms, but Sir Peter catches her and tells her to make sure she serves the elvish mushrooms.