Heat oven to 350°F. Grease 13x9-inch pan. Lightly spoon flour into measuring cup; level off. In large bowl, combine all base ingredients; beat at low speed until crumbly. Press mixture in bottom of greased pan. Bake at 350°F. for 12 to 14 minutes or until light brown.
Meanwhile, in small bowl, combine all filling ingredients except walnuts; beat until well combined. Stir in walnuts.
Remove pan from oven; pour filling evenly over warm base. Return to oven; bake at 350°F. for an additional 20 to 30 minutes or until filling is set. Cool 1 hour or until completely cooled.
In small bowl, combine all glaze ingredients; blend until smooth, adding enough milk for desired drizzling consistency. Drizzle evenly over bars. Cut into bars. Store in refrigerator.