peanut butter in bowl of electric mixer. Beat until combined (batter will be stiff). By hand, stir in chocolate chips. Transfer batter to prepared pan. Bake on middle rack of oven for 30 minutes or until a toothpick inserted into center comes out clean. Let cool in pan on wire rack. Cut squares. Tester's note: This is a dense, brownielike cake that needs no frosting. ----