In a medium bowl, combine flour, sugar, baking soda, and salt; cut in shortening and 1/2 cup peanut butter until mixture resembles coarse crumbs.
Blend in corn syrup and milk.
Shape into 2 x 12 - inch log.
Chill 1 to 2 hours or until firm enough to slice.
Preheat oven to 350°F.
Slice dough into 1/4 - inch thick rounds. Place half of rounds 2 inches apart on ungreased cookie sheets; spread each round with 1/2 teaspoon peanut butter.
Cover with remaining rounds to form a sandwich; seal edges with a fork.
Bake at 350°F for 10 to 12 minutes or until browned. Cool on wire cooling racks.