The primary ingredient in a chocolate cake is cocoa powder or melted chocolate. These elements provide the cake with its rich chocolate flavor. Generally, chocolate cakes are made using a combination of flour, sugar, eggs, butter, and a leavening agent, with cocoa or chocolate being the key ingredient that defines the cake's character. Variations might include adding milk or cream for moisture or different types of chocolate for varying intensities of flavor. The result is a beloved dessert enjoyed worldwide.