Combine first 3 ingredients; cook 5 minutes. Transfer berries to a bowl using a slotted spoon. Combine cornstarch and water; add to blueberry liquid, and bring to a boil. Boil 1 minute; stir in blueberries. Chill.
Coat a 9-inch round cakepan with cooking spray. Dust with 1 teaspoon flour. Combine remaining flour, baking powder, and salt. Beat margarine at medium speed of an electric mixer until creamy; add 1/3 cup sugar, beating well. Add egg yolk, beating just until blended. Add flour mixture to creamed mixture alternately with milk. Mix well after each addition. Stir in vanilla.
Beat egg whites at high speed of electric mixer until foamy. Add remaining sugar, 1 tablespoon at a time, beating until stiff peaks form. Stir 1/2 cup egg white into batter; fold in remaining egg white. Spoon into pan. Bake at 350° for 30 minutes. Cool on a wire rack 10 minutes. Remove from pan; let cool on wire rack. Slice in half horizontally. Drain blueberries, reserving half of juice. Drizzle juice over bottom layer. Spread 3/4 cup whipped topping over cake layer; spoon half of blueberries over topping. Top with remaining cake layer. Repeat procedure with remaining 3/4 cup topping and blueberries.