Pies may be classified into two groups based on method of assembling and baking.
Baked Pies. Raw pie shells are filled and then baked. Fruit pies contain fruit fillings and usually have a top crust. Soft pies are those with custard-type fillings—that is, liquid fillings that become firm when their egg content coagulates. They are usually baked as single-crust pies.
Unbaked Pies. Prebaked pie shells are filled with a prepared filling, chilled, and served when the filling is firm enough to slice. Cream pies are made with pudding or boiled custard-type fillings. Chiffon pies are made with fillings that are lightened by the addition of beaten egg whites and/or whipped cream. Gelatin or starch gives them a firm consistency.