Place the powdered sugar, flour, cornstarch, almond flour, butter and almond extract into a mixing bowl with a paddle and mix until they come together. Roll into a log, cut into small pieces and roll into balls. Chill for a 1/2 hour. Spray small deep tart molds with oil and place 1 ball in the center of each mold. Bake in a preheated 375 degree oven for about 15 minutes until light golden brown. Take them from the oven and make a depression in the center by pressing the handle of a wooden spoon into the baked dough. Make the indentation big enough to hold a blueberry. Let cool and carefully remove from molds. In a small saucepan bring the maple syrup to a boil. Turn off the heat and add the blueberries stirring gently to lightly cook them. Place 1 berry in the center of each shortbread cup and sprinkle with powdered sugar.