Macerate the berries: Place the berries in a mixing bowl. Toss with sugar and Grand Marnier. Put in the fridge for at least an hour to let the juices blend. Add in a little orange juice if you like for a juicier mix.
Preheat an oven to 425 degrees F
Make the biscuits: Mix all the dry ingredients in a mixing bowl. For the best results work the dough by hand. Cut the butter in to pea sized pieces. The colder the butter the better. Another method is to use a hand grater. Mix the butter into the flour well.
Add in the buttermilk and incorporate well. Mix the dough until it stays together and is not too sticky. But, don't over-mix or it will become tough and won't rise well.
Place dough on a floured surface and form into a rectangle with your hands. Some people use rolling pins. That will cut down on the fluffiness of the dough. Use your hands. Smooth the dough out to about 3/4 inch.
Fold the dough onto itself. You will want extra flour to flour the surface so things don't stick too much. Fold in thirds: picture the dough in 4 sections. Fold the 1st quarter on top from the left side and the last quarter in from the right. Then press the dough back into a rectangle about 3/4 inch high again. Repeat this folding procedure 2 more times. This will create layers in the dough that will puff up nicely.
Put a nonstick sheet in a sheet pan or use waxed paper or parchment paper. Spray with pan spray. Cut out the biscuits with a cutter. When you cut them, be careful not to twist the cutter or press down on the sides if you use a knife. That will seal the sides and they won't rise as well as you would like.
Place the biscuits in the pan and brush the tops of each with a little buttermilk and sprinkle with sugar. Bake for 10 to 15 minutes until golden brown and fluffy. Remove from heat and allow to cool.
make the whipped cream: In a mixer or by hand, whip the cream until it begins to stiffen. When you have soft peaks, add in the sugar, vanilla, and Grand Marnier. Continue whipping until firm peaks occur. Do not over-whip or it will break down. I prefer just past the soft peak stage.
Split the biscuits with a bread knife. Place the bottom in a bowl, spoon in berries, top with whipped cream, then put the top of the biscuit on. Garnish with powdered sugar and a sprig of fresh mint. Serve immediately.