Heat oven to 350°F (325°F for dark or nonstick pan). Line 9-inch square pan with foil, allowing some to hang over edges of pan. Grease bottom and sides of foil with shortening or cooking spray. Make and bake brownies as directed on box. Top hot brownies evenly with peanut butter cup candies, 4 rows by 4 rows; press down slightly. Cool completely on cooling rack, about 1 1/2 hours. If necessary, refrigerate 30 minutes, until peanut butter cups are firm.