Medieval cooks had restricted access to ovens due to their costs of construction and need for abundant supplies of fuel. Pies could be easily cooked over an open fire, while partnering with a baker allowed them to cook the filling inside their own locally defined casing. The earliest pie-like recipes refer to coffyns (the word actually used for a basket or box), with straight sealed sides and a top; open-top pies were referred to as traps. The resulting hardened pastry was not necessarily eaten, its function being to contain the filling for cooking, and to store it, though whether servants may have eaten it once their masters had eaten the filling is impossible to prove.[6] This may also be the reason why early recipes focus on the filling over the surrounding case, with the partnership development leading to the use of reusable earthenware pie cases which reduced the use of expensive flour.[7]