Using a 3-inch bowl or cookie cutter, draw 8 circles on a sheet of parchment paper. Turn the paper over, and place on a baking sheet; set aside.
Preheat oven to 200 degrees. In the bowl of an electric mixer fitted with the whisk attachment, combine whites, lemon juice, and vanilla. Beat on medium-low speed until soft peaks form, about 1 1/2 minutes. Reduce to low speed, and gradually sprinkle sugar over whites. Increase speed to high and beat until stiff glossy peaks form, 2 to 3 minutes. Remove from mixer; sift cornstarch over, and fold to combine.
Fit a pastry bag with a plain pastry tip with a 1/2-inch opening (Ateco #6), and fill bag with meringue. Beginning in the center of one of the circles, cover with an even layer of meringue. Pipe around the perimeter to form a 1-inch collar. Repeat process with remaining circles.
Transfer baking sheet to oven, and bake for 1 hour. Reduce heat to 175 degrees and bake until meringue has dried but is still white, about 1 hour more. Transfer to a wire rack to cool.
Place a meringue on a dessert plate. Fill with a scoop of sorbet, and drizzle with blueberry sauce. Serve immediately.