Prepare the Sauce: In a skillet, combine blackberries, sugar, water, lemon juice, cinnamon, and vanilla. Stir over medium heat until simmering, about 5 minutes.

Mix the Dry Ingredients: In a bowl, whisk together flour, baking powder, cinnamon, salt, and sugar until well combined.

Cut in Butter: Add butter to the dry mixture and blend until it resembles coarse crumbs.

Combine Wet Ingredients: Mix buttermilk and vanilla in a measuring cup, then pour into the flour mixture until just combined.

Form the Dumplings: Scoop tablespoonfuls of dough onto the simmering sauce in the skillet. Ensure they are spaced evenly.

Simmer the Dumplings: Cover the skillet and reduce heat to low. Let them simmer for 12-14 minutes.

Serve the Dumplings: Remove from heat and cool slightly. Serve warm with optional ice cream or whipped cream.