A pancake is a batter cake fried in a pan or on a griddle with oil or butter. Pancakes can be eaten hot or cold, and are generally filled or topped with a sweet or savoury sauce or condiment. Most types of pancake batter contain some kind of flour, most commonly wheat flour, or buckwheat flour, and a liquid ingredient, such as water, milk, or ale, although pancakes are sometimes made with cornmeal in the U.S. and potato pancakes are also popular in various European countries, such as Germany and Poland. In some countries, such as Egypt, Canada and the United States, pancakes contain a raising agent, such as baking soda or yeast. The batter of the Ethiopian injera is left to ferment in order to achieve a similar effect. The oldest surviving pancake recipe in the English language dates from the 15th century.