HEAT oven to 350 degrees F. Coat an 8-inch springform pan with no-stick cooking spray.
PREPARE brownie mix according to package directions using packet of chocolate-flavored syrup, oil, water and egg. Spread into prepared pan. Bake 34 to 37 minutes or until toothpick inserted in center comes out clean. Cool completely on wire rack.
BEAT peanut butter and vanilla in medium bowl with an electric mixer until smooth. Gradually add powdered sugar. Beat for 1 minute. Remove outer edge of springform pan. Spread peanut butter mixture over top of cooled brownie. Chill 30 minutes or until firm.
PLACE hot fudge topping in small resealable plastic bag. Knead until smooth. Cut small corner off bag. Drizzle topping over peanut butter layer. Cut into wedges.