In a saucepan, combine the lemon juice, 3/4 cup sugar, salt and 2 cups of water. Bring the liquid to a boil. In a small mixing bowl, whisk the eggs, cornstarch and remaining 1/2 cup of water, together. Spoon 1/2 cup of the hot liquid into in the egg mixture, whisking constantly. Whisk the egg mixture into the lemon mixture and bring back to a boil. Cook the mixture for about 4 minutes, or until thick, whisking constantly. Pour the mixture into the pie shell and cool completely. Using an electric mixer, fitted with a whip attachment, whip the egg whites until soft peaks form. Add the remaining 2 tablespoons of sugar and continue to whip until firm peaks form. Spread the mixture evenly over the pie. Place in the oven until the top is golden, about 3 to 4 minutes. Remove from the heat and cool. Spoon the coulis in the center of each plate. Place a piece of the pie in the center of the sauce. Garnish with powdered sugar and mint.