In a large, heavy-bottom saucepan, combine blackberries (2 quarts), sugar (1 cup), water (1 1/2 cups), butter (2 tablespoons), nutmeg (1/2 teaspoon), cinnamon (1/2 teaspoon), and lemon juice (2 teaspoons). With the saucepan uncovered, bring to a boil, then reduce heat until you have a light boil. Stir frequently so the sauce doesn't burn, until the fruit begins to break down and the sauce thickens enough to coat the back of a spoon, about 25-35 minutes (The blackberries will continue to cook and break down after the dumplings are added. You don't want the fruit to break down too much, at this point).
As the sauce is cooking, begin the dumplings. In a large mixing bowl, add flour (1 1/4 cups), sugar (1/4 cup), baking powder (1 1/2 teaspoon), salt (1/2 teaspoon), and cinnamon (1/4 teaspoon) then whisk to evenly combine.
Stir in the milk (3/4 cup) with a large spoon just until it comes together to form a sticky wet dough. Let the dough set for about five minutes.
Drop the dough by the spoonful into the blackberry sauce. Reduce heat to medium and continue to simmer, covered, until the dumplings are springy and cooked through.
Flip dumplings in sauce if desired. Serve warm with a scoop of ice cream!
Notes
Is It Done Yet? Once the blackberry syrup ingredients are simmering, stir frequently. Simmer until the volume is reduced by about half and coats the back of a spoon.
Other Berries? You may use other berries, but blackberries are traditional.
Make Them Springy: The dumplings are done when they spring back when touched.