A custard pie is any type of uncooked custard mixture added to an uncooked or partially cooked crust and baked together. In North America, custard pie commonly refers to a plain mixture of milk, eggs, sugar, salt, vanilla extract and sometimes nutmeg combined with a pie crust. It is distinctly different from a cream pie, which contains cooked custard poured into a cooled, precooked crust. In the United Kingdom, the comical or political act of pieing is conventionally done with a "custard pie". Some common custard pies include pumpkin pie, lemon and buttermilk chess pie, coconut cream pie, and buko pie. True custard is defined as a liquid thickened with eggs. Due to the often large number of whole eggs in custard pie it is a very rich pie.
The Ancient Romans were the first to understand the binding properties of eggs. During the Middle Ages, the first custard pies, as we know them, began to appear. Initially, custards were used only as fillings for pies, pastries and tarts. Both Europe and Asia had recipes that contained custards. The word custard is derived from ‘crustade’ which is a tart with a crust.