Lemon meringue pie is a type of baked pie, usually served for dessert, made with a crust usually made of shortcrust or shortbread pastry, lemon curd filling and a fluffy meringue topping. Lemon meringue pie is prepared with a bottom pie crust, with the meringue is directly on top of the lemon filling. No upper crust is used, as in a cherry pie.
The lemon custard is usually prepared with egg yolks, lemon zest and juice, sugar, and starch. This gives it a texture similar to that of a sturdy pudding. The meringue, which includes well beaten egg whites and sugar, is cooked on top of the pie filling. As the meringue bakes, air bubbles trapped inside the protein of the egg whites will expand and swell. However, if the egg whites are beaten too much, or if a tiny amount of fat is allowed to contaminate the mixture, then the proteins will not be able to form the correct molecular structure when cooked, and the meringue may collapse when cooked. The meringue can be beaten into either soft or stiff peaks. The temperature the pie is baked at and the method sugar is added also determines the texture and durability of the meringue.