Preheat oven to 200ºC . In a nonreactive saucepan, toss the blueberries and granulated sugar. Cook over moderately high heat, stirring occasionally, until the juices begin to bubble, 3-5 minutes; do not overcook or the berries will burst. Pour into a stainless steel strainer set over a bowl. Reserve the drained juices. Using an electric mixer, beat the egg yolks with 4 tablespoons of the superfine sugar until pale and thick, about 2 minutes. Gradually beat in the lemon juice and then the zest. Transfer the mixture to a nonreactive saucepan and cook over low heat, stirring, until it thickens, about 8 minutes; do not boil. Scrape into a bowl and set aside on a rack to cool. Using clean beaters, beat the egg whites until foamy. Add the salt and beat until soft peaks form. Add the remaining 3 tablespoons superfine sugar, half tablespoon at a time, beating well after each addition. Beat at high speed until the whites are glossy but not dry, about 20 seconds longer. Using a rubber spatula, stir one-fourth of the beaten whites into the yolk mixture. Gently fold in the remaining whites in three additions. Spoon the blueberries into the pie shell and drizzle 2.5 tablespoons of the drained juices over them. Mound the souffle mixture over the berries, touching the pie crust all around. Bake in the middle of the oven for about 15 minutes, until the top is nicely browned. Transfer the pie to a rack to cool slightly. Serve at warm or at room temperature.