Preheat oven to 375°.
In a 10 – inch cast iron skillet, stir together the blackberries, brown sugar, orange juice, vanilla, cardamom and orange peel over medium-high heat. Bring to a simmer, and cook until juice is released from blackberries and mixture is hot and bubbly, approximately 10 minutes.
In a small bowl, whisk together cornstarch and 3 tablespoons water. Slowly add to berry mixture, stirring to combine. Cook until thickened, about 3 minutes. Remove from heat.
In a medium bowl whisk together flour, sugar, baking powder and salt. Add butter. Combine with fingertips until crumbly. Add cream and stir gently until biscuit like dough forms.
Tear dough into 3-inch round pieces: arrange over berries. Sprinkle with sanding sugar.
Bake until topping is lightly browned, 30 minutes.