Pour the heavy cream into a large bowl with half of the confectioners' sugar and almond extract. Whip until stiff. Fold in sour cream. Refrigerate.
In a separate bowl, toss blackberries with the remaining confectioners' sugar. Let stand at room temperature for about 15 minutes.
In 8 parfait glasses, layer whipped cream and blackberries, beginning and ending with whipped cream. Garnish each parfait with a strip of lemon zest, a few blackberries and a sprig of mint.
