Heat oven to 350°F. Line cookie sheets with cooking parchment paper or lightly spray with cooking spray.
In large bowl, beat cookie ingredients with electric mixer on low speed until moistened; beat 1 minute longer on high speed. Drop batter by 1/4 cupfuls 2 inches apart onto cookie sheets.
Bake 13 to 16 minutes or until set (do not overbake). Cool 2 minutes; remove from cookie sheets to cooling racks. Cool completely, about 15 minutes.
In large bowl, beat filling ingredients with electric mixer on high speed until light and fluffy. For each sandwich cookie pie, spread about 1/4 cup filling on bottom of 1 cooled cookie. Top with blueberries, raspberries and second cookie, bottom side down. Store covered in refrigerator.