Combine cookie mix, butter and egg in medium bowl; mix well.
Shape dough into 4 (6x1-inch) logs on lightly floured surface. Wrap in plastic food wrap; refrigerate at least 2 hours or until firm.
Heat oven to 375°F. Reshape logs, if necessary. Cut each log into 16 (about 1/4-inch) slices with sharp knife. Place 2 inches apart onto ungreased cookie sheets. Bake 8-10 minutes. Cool 1 minute on cookie sheet; remove to cooling rack. Cool completely.
Spread 1/2 teaspoon each peanut butter and jam on flat-side of 1 cookie. Top with second cookie, flat-side down. Press together slightly. Repeat with remaining cookies.
- The jam and peanut butter filling will soften the cookies, so if you like them crisp, assemble sandwich cookies just before eating.
- If desired, you can fill cookies with just peanut butter or just jam.