Parkin is a traditional gingerbread cake that originated in northern England, often associated with Yorkshire but also popular in Lancashire). It is made with oatmeal and black treacle (molasses), and flavored with ginger and other spices. Parkin is traditionally eaten on Guy Fawkes Night, 5 November, and when celebrating Yorkshire Day on 1st August, but is also enjoyed throughout the winter months). The cake is baked commercially throughout Yorkshire, but is mainly a domestic product in other areas). The flour used in parkin in England is self-raising, containing a small amount of chemical leavening agent. If this is not available, or if the proportion of oatmeal is high, it is essential to add a leavening agent, e.g. baking powder or a mixture of sodium bicarbonate and cream of tartar). The cake is known for its sticky, chewy texture and is said to improve with age.