1. Heat oven to 350 degrees F. Coat 12-cup (10-inch) Bundt pan with nonstick cooking spray.
2. Onto waxed paper, sift together cake flour, baking powder and salt. With an electric mixer, beat the butter in medium-size bowl until smooth. Beat in sugar until light and fluffy, 2 to 3 minutes. Beat in eggs, one at a time. Stir in lemon rind and vanilla. Alternately beat flour mixture and lemonade in 3 batches into butter mixture, beginning and ending with flour. Fold in blueberries. Scrape batter into prepared pan.
3. Bake in 350 degrees F oven for 45 to 50 minutes or until the top is golden and a wooden pick inserted in the center comes out clean.Meanwhile, prepare sauce:
4. Combine blueberries, sugar, cornstarch and water in medium-size saucepan. Cook over medium heat until sugar is dissolved, liquid is cleared and blueberries begin to burst, 5 to 7 minutes. Transfer mixture to food processor or blender. Puree until smooth. Let cool.
5. To serve, cut cake into slices and drizzle with warm or room-temperature blueberry sauce.