Preheat the oven to 350 degrees. Spray a 9-inch tart pan with removable bottom with cooking spray. Line the tart pan with the pie crust.
Put the almond paste in the bowl of an electric mixer and beat until smooth. Add the egg, sugar, butter, flour, vanilla and almond extracts, and salt. Beat on medium-high speed until smooth. Scrape the mixture into the prepared tart pan. Top with the grapes and bake for 30-35 minutes or until golden brown. Let cool in the pan. Remove the outer ring, dust with powdered sugar, and serve.