1Heat oven to 350°F. Lightly grease bottom and sides of 15x10x1-inch pan with shortening or cooking spray.
2In large bowl, beat all bar ingredients except raisins with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Stir in raisins. Spread in pan.
3Bake 20 to 25 minutes or until light brown. Cool completely in pan on cooling rack, about 2 hours.
4Spread frosting over bars. Sprinkle with walnuts. For bars, cut into 7 rows by 7 rows. Store in refrigerator.