HEAT oven to 325 degrees F. Spray an 8 x 8-inch baking pan with no-stick cooking spray.
BEAT butter until soft and creamy. Gradually add sugar, beating until mixture is light and fluffy. Add egg yolks, beating until well blended. Gradually add flour, mixing thoroughly. Fold in nuts.
SPREAD half of batter evenly into prepared pan. Spread with preserves. Top with remaining batter dropped by spoonfuls.
BAKE 50 to 60 minutes or until lightly browned. Cool. Cut into 2 x 1-inch bars.