1Heat oven to 375°F. In large bowl, stir cookie mix, softened butter, egg and flour until soft dough forms.
2Gently fold in strawberries and blackberries. Drop by about 40 two-level-teaspoonful portions 2 inches apart on ungreased cookie sheet.
3Bake 8 to 10 minutes or until cookies are set. Cool 1 to 2 minutes; remove from cookie sheet to cooling rack. Cool completely, about 30 minutes.
4Spread bottom of 1 cookie with frosting. Top with another cookie, bottom side down. Do not press together. Sprinkle with powdered sugar. Repeat to use up cookies.