Butter six 8-ounce ramekins and dust with sugar. Set aside.
Preheat oven to 400º. Set ramekins on a baking sheet.
Coarsely puree half the berries with 6 tablespoons of sugar, lemon juice and cornstarch. Pour into a small saucepan and cook on medium till puree boils and thickens. Cool completely.
Slice the remaining berries and add 2 tablespoons of sugar and 1 teaspoon of Grand Marnier. Mix and taste for sweetness. Add more sugar if needed. Set aside.
Beat egg whites till foamy.
Slowly add in the remaining 3 tablespoons of sugar and whip till stiff peaks form.
Slowly fold puree into egg whites, one-third at a time.
Divide between the six ramekins and smooth tops with an offset spatula. Run a finger around the perimeter of each soufflé to make a slight indentation in the soufflé.
Slide the tray of ramekins into the oven and bake for 14-17 minutes or till soufflés are puffed and golden.
Serve immediately with sliced berries.
