Heat oven to 350°F. Combine all crust ingredients in small bowl. Beat at low speed, scraping bowl often, until mixture resembles coarse crumbs. Press onto bottom of ungreased 8-inch square baking pan. Bake for 15 to 20 minutes or until edges are lightly browned.
Meanwhile, combine all filling ingredients except powdered sugar in small bowl. Beat at low speed, scraping bowl often, until well mixed. Pour filling over hot, partially baked crust. Continue baking for 18 to 20 minutes or until filling is set.
Sprinkle with powdered sugar while still warm and again when cool. Cut into bars.
Gluten-Free Flour Blend: To make Flour Blend, combine 2 cups rice flour, 2/3 cup potato starch, 1/3 cup tapioca flour and 1 teaspoon xanthan gum. Store in container with tight-fitting lid; stir before using.