Set aside 6 beautiful berries for garnish and slice the remaining berries. In a mixing bowl toss the strawberries with the sugar and Grand Marnier. Set aside to macerate at least 15 minutes, and up to 1 hour. Meanwhile, whip the cream to soft peaks. Split the biscuits, mound the strawberries on bottom half, top with a dollop of whipped cream and replace the biscuit top. Garnish with mint sprigs. Dip the remaining berries into the chocolate and use to garnish plate.