In a large skillet, combine blackberries, granulated sugar, water, lemon juice, ground cinnamon, and vanilla extract. Stir well and heat until gently simmering.

In a mixing bowl, whisk together flour, baking powder, cinnamon, salt, and sugar. Cut in cold butter until it resembles coarse crumbs. Mix buttermilk with vanilla and stir into the flour mixture to form a shaggy dough.

Drop tablespoon-sized dollops of the dough onto simmering blackberry sauce, cover, and reduce heat. Cook for 12-14 minutes without lifting the lid.

Remove the lid and let the dumplings cool slightly. Serve with blackberry sauce and top with ice cream or whipped cream if desired.