Line 9-inch square pan with foil, with ends of foil extending over sides; spray with cooking spray. Beat peanut butter, butter and sugar in large bowl with mixer until blended.
Add eggs and vanilla; mix well. Beat in flour and salt. Stir in chocolate and nuts.
Pour into prepared pan. Drop jam by spoonfuls over batter; swirl gently with knife.
Bake 35 to 40 min. or until toothpick inserted in center comes out with fudgy crumbs. (Do not overbake.) Cool completely. Use foil handles to remove brownie from pan before cutting to serve.