In a 10-inch cast-iron skillet, stir together blackberries, brown sugar, orange juice, vanilla, and cardamom; bring to a boil over medium-high heat. Reduce heat, and simmer until juice is released from berries and mixture is hot and bubbly, about 10 minutes.
In a small bowl, stir together cornstarch and 3 tablespoons water. Slowly stir cornstarch mixture into berry mixture; cook until thickened, about 3 minutes. Remove from heat.
In a medium bowl, whisk together flour, granulated sugar, baking powder, and salt. Using a pastry blender, cut in cold butter until mixture is crumbly. Stir in cream just until dry ingredients are moistened. Drop dough by 3-inch round pieces onto berry mixture, and sprinkle with sanding sugar.
Bake until topping is lightly browned, about 30 minutes. Let cool for 30 minutes before serving.
Recipe by Paula Deen Magazine at https://pauladeenmagazine.com/skillet-blackberry-cobbler-recipe/