1Heat oven to 350°F (325°F for dark or nonstick pan). Grease bottom only of 9-inch square pan with shortening or cooking spray. (For easier cutting, line pan with foil, then grease foil on bottom only of pan.) Make brownies as directed on box. Cool completely, about 1 hour.
2In small microwavable bowl, microwave frosting uncovered on High about 10 to 15 seconds or until drizzling consistency. Drizzle frosting over brownies; sprinkle with star decors. For brownies, cut with plastic knife into 4 rows by 4 rows. Store covered at room temperature.