Beat heavy cream and confectioners sugar until stiff peaks form. Stir yogurt until very smooth, then fold into whipped cream. Chill until proceeding with assembly, but prepare no more than 4 hours ahead.
In a large bowl, toss together the strawberries, raspberries, blueberries, sugar and liqueur, if using. Refrigerate until serving.
Remove cream filling and berry mixture from refrigerator. Add mint to berries. Divide cream filling evenly among dessert shells. Top with fresh berries.