Heat oven to 350°F. Butter a 13 x 9 x 2-inch baking pan.
Beat flour, sugar, yolks, butter and lemon rind in medium-size bowl until dough forms. Set aside about 3/4 cup dough. Pat remaining dough into bottom of prepared pan and slightly up sides. Spread with jam. Sprinkle reserved dough over top for crumbs.
Bake in 350°F oven for 45 minutes. Let cool completely in pan on wire rack. Cut into 32 squares. Store in tightly sealed container, or wrap in aluminum foil.