Preheat oven to 375 F.

Line a 10-inch tart pan with pastry. Arrange grapes snugly in decorative rings in pastry. With an electric mixer combine almond paste, egg, sugar, butter, flour, and salt until smooth to create frangipane. Carefully spread over arranged grapes and bake for 35 minutes, until the tart is golden brown and cooked through. If using a convection oven, bake at 350 F for 30 minutes. When tart is cool, remove from pan and dust with confectioners sugar.