Preheat oven to 400°F and lightly grease 6 to 8 eight-ounce ramekins or a square pan. If baking individual ramekins, set in a foil lined baking pan, if making in one pan, set on a sheet pan for easy cleanup.
Stir together the blackberries, sugar, cinnamon, salt, cornstarch, and butter in a large bowl. Then, divide the berry mixture among the ramekins or transfer to the prepared baking pan. Bake for 12-15 minutes or until it begins to bubble.
Ginger Biscuits
Whisk together baking powder, salt, flour, and 3 tablespoons of sugar in a large bowl. Cut butter into the flour mixture using a pastry blender until it resembles small peas. Add crystallized ginger and cinnamon, tossing to combine.
Pour in the buttermilk, stirring just until the dry ingredients are moistened. Turn the dough out onto a lightly floured surface and knead 3 to 4 times. Pat into a 3/4-inch-thick rectangle (about 7 by 5 inches). Cut into 6 pieces, about 3 by 2 1/2 inches.
Remove the ramekins or baking pan from the oven and carefully place the biscuit dough over the hot filling in the ramekins or baking dish. Brush the dough with the beaten egg and sprinkle with the remaining sugar. Return to the oven and bake until the fruit is bubbly and the biscuits are golden, 22 to 25 minutes. Let stand 20 minutes. Top with vanilla ice cream if desired.