In a cast-iron skillet, combine fresh or frozen blackberries, granulated sugar, water, lemon juice, ground cinnamon, and vanilla extract. Heat over medium heat, stirring gently until the mixture begins to simmer, about 5 minutes.

In a mixing bowl, whisk together the flour, baking powder, remaining sugar, salt, and a pinch of cinnamon. Cut in the cold, unsalted butter until the mixture resembles coarse crumbs. Gradually mix in the buttermilk and a touch of vanilla extract, stirring just until combined.

Once your blackberry sauce is bubbling, drop tablespoonfuls of the dumpling dough directly into the simmering mixture. Cover the skillet with a lid and reduce the heat to low. Let the dumplings cook for 12-14 minutes, or until fluffy.

Gently remove the skillet from heat and let the Blackberry Dumplings cool for a moment. Serve warm in bowls with the rich blackberry sauce and a scoop of vanilla ice cream or whipped cream.