Combine blackberries, water, and sugar in a large pot or in a deep cast iron skillet. Over medium heat, mix and bring to a boil. Let the blackberry mixture boil for 2-3 minutes and turn off heat.

In a bowl, whisk together the flour, sugar, salt, and baking powder. In a separate bowl, whisk together the milk, butter, egg, and vanilla. Pour the wet mixture into the center of the dry ingredients and mix until it just comes together in a sticky, wet dough. Do not over mix.

Return the sauce to a boil over medium heat. Drop the dough by spoonful into the simmering sauce. The dumplings should be side by side and not on top of each other.

Place a lid on the pan and lower the heat to medium low. Simmer, fully-covered for 15-20 minutes. Do not lift the lid while simmering (this is very important). After 15-20 minutes, remove the lid and check the dumplings by cutting into one with a fork. They should be fluffy, not sticky, in the center.

Once done, flip the dumplings to make sure all sides are coated in the blackberry sauce.

Serve warm with a scoop of vanilla ice cream.