Toss strawberries, blueberries, sugar, Grand Marnier (if using), orange zest and cinnamon together. Let sit for at least 20 minutes or up to a day.
1
Stir together flour, sugar, baking powder and salt. Add the grated butter and stir just until the butter is incorporated.
2
Add buttermilk to the flour mixture and then turn out onto the counter and form the dough into a rectangle.
3
Fold the dough on the left and right sides. Flatten the dough, rotate and repeat three times to build flaky layers.
4
Cut out the shortcakes with a cookie cutter, brush with more buttermilk and bake in a hot oven.
5