Coat 9" glass pie plate with non-stick spray.Melt butter and brown sugar in a large sauce pan over medium heat until mixture starts to boil.Remove from heat; cool 10 min.
Stir in 1 egg and vanilla until well blended,then stir in flour and baking powder until smooth. Scrape (don't spread)3/4 cup into prepared pie plate;freeze 10 min.or until firm.
Meanwhile heat oven to 350 degrees and melt 1/2 cup chocolate chips as package directs. Stir melted chips,remaining egg and cocoa powder into remaining batter.
Press chilled batter evenly over bottom and halfway up sides of pie plate.Top with Milky Way, than chocolate batter.
Bake 24 to 27 min. until tooth pick inserted in center comes out with moist crumbs attached. Sprinkle remaining 1/2 cup chocolate chips in middle, let stand 5 min. until soft, then spread to blondie crust in decorative swirls. Top with garnishes. Cool before cutting into wedges.