Heat oven to 350°F. Line 13x9-inch pan with foil, extending foil over sides of pan. Grease bottom only of foil. In large bowl, combine all brownie ingredients; beat 50 strokes with spoon. Spread batter in greased foil-lined pan.
Bake at 350°F. for 28 to 30 minutes or until set. DO NOT OVERBAKE. Cool 1 hour or until completely cooled. Freeze brownies 30 minutes.
Remove brownies from pan by lifting foil. Cut into 1 1/4-inch squares. Return to freezer while preparing icing.
In medium saucepan, melt chocolate chips over very low heat, stirring constantly. Add frosting and vanilla; mix well to combine. Heat 1 to 2 minutes or until of desired coating consistency, stirring constantly. Remove from heat.
To coat each brownie with icing, place brownie on fork over saucepan; spoon icing over brownie, coating all sides except bottom. (If icing thickens, heat over low heat until of desired consistency). Decorate as desired with decorator frosting.