In a sauce pot, over high heat, reduce the balsamic vinegar by 2/3 or until syrup consistency, about 20 minutes. In a saute pan, heat the butter. When the butter has melted, saute the berries for 1-2 minutes. Stir in the raspberry coulis and balsamic vinegar. Bring the sauce up to a simmer and remove from the heat. Place a scoop of the sorbet in the center of a shallow pasta bowl. Spoon 1/4 of the mixture over the sorbet. Garnish with the white chocolate sauce, mint and powdered sugar.