Ina small bowl, combine flour and salt, cut the shortening until crumbly. Gradually add water, tossing with a fork until dough forms a ball. Cover and refrigerate for at least 30 minutes.

Divide dough in half. Roll each half into a 6-inch circle. Transfer to two 4 1/2 inch tart pans, fit pastry into pans trimming if necessary. Arrange pecans in shells.

In another small bowl, whisk egg, brown sugar, corn syrup, and vanilla. Pour over pecans. Place shells on a baking sheet, bake 375F for 35-40 minutes or until a knife inserted in the center comes out clean. Cool on a wire rack. Top with whipped cream if desired.