Heat oven to 350°F. Coat 15-1/2 x 10-1/2 x 1-inch jelly-roll pan with cooking spray. Line with waxed paper; coat paper with spray. Dissolve coffee granules in water in small bowl.
Beat butter and sugar at medium speed in large bowl until combined, 3 minutes. Add corn syrup; beat until smooth. Beat in eggs, coffee mixture and vanilla.
Combine flour, baking powder, cinnamon and salt in medium bowl. On low speed, beat in flour mixture alternately with sour cream, ending with flour mixture. Fold in chips and walnuts. Spread in prepared pan.
Bake in 350°F oven for 30 minutes or until center is set. Let cool in pan on wire rack. Spread with prepared chocolate frosting. Cut into 2-inch squares and serve.