4 ripe bananas
1/2 cup buttermilk, divided
1/2 to 3/4 cup sifted powdered sugar, divided
1 tsp. lemon juice, divided
1 pkg. (16 oz.) frozen mixed berries, peaches, pitted cherries, or mango (3-1/2 cups fruit)
Rolled butter cookies for garnish
Place unpeeled bananas in freezer for 2 hours or up to 4 hours before serving. Unpeel frozen bananas, cut into 1/2-inch chunks. Combine 1/4 cup buttermilk, 1/4 cup sugar, and 1/2 tsp. lemon juice in blender or food processor container. Cover; process until blended. Drop one half banana chunks through hole in lid of blender or food processor tube, with machine running, until blended. Add half the fruit pieces, a few at a time, and process until mixture is slushy, stopping machine occasionally to scrape down sides of bowl. Transfer mixture to chilled bowl. Repeat with remaining ingredients (adding more sugar if desired to taste) to make a second batch. Add to remaining mixture in bowl and stir together. If preparing ahead, cover mixture and freeze immediately for up to 2 hours before serving. Spoon into serving dishes to serve. Garnish each serving with a butter cookie.