Heat oven to 350°F. In large bowl, mix cookie mix, butter, flour and 1 egg until soft dough forms. Shape dough into 20 (1 1/2-inch) balls. Press thumb into center of each ball to form indent. Press 1 brownie ball into center of each cookie, making sure to form dough around brownie ball to enclose; reshape balls. Place 2 inches apart on ungreased large cookie sheets.