Preheat oven to 300 degrees. Add the egg whites and salt to a mixing bowl. Beat on medium until soft peaks form. Add the sugar and continue to beat until very stiff peaks form. Fill your pastry bag with the meringue, handing it gently. Pipe out 8 3-inch diameter rings on the lined sheet tray. You want to pipe it so the middle is free to be filled later. Place in the oven and cook for 35 minutes. Turn off the oven and allow to sit for 1 hour. Serve with the berries, cream and mint.