Step 1: In a large, wide saucepan, combine 1 quart of fresh or frozen blackberries, 1 cup of water, 1 cup of sugar, 1/4 teaspoon of salt, and 1/2 teaspoon of lemon extract. Bring this mixture to a boil over medium heat, then reduce the heat and let it simmer gently for 5 minutes.
Step 2: While the sauce simmers, prepare your dumplings. In a separate mixing bowl, whisk together 1 1/2 cups of all-purpose flour, 1 tablespoon of sugar, 2 teaspoons of baking powder, 1/4 teaspoon of salt, and 1/4 teaspoon of nutmeg. Gradually add 2/3 cup of milk, stirring until the ingredients are just combined. Be careful not to overmix the batter.
Step 3: Using a tablespoon, carefully drop spoonfuls of the dumpling batter into the simmering berry mixture. Once all the batter is added, cover the saucepan tightly with a lid and let it simmer for precisely 15 minutes. It's crucial not to lift the lid during this time, as the steam is essential for cooking the dumplings through.
Step 4: Once cooked, remove the saucepan from the heat. Serve the blackberry dumplings immediately, while they are warm and tender. They're wonderful on their own, or you can elevate them with a scoop of vanilla ice cream or a dollop of fresh whipped cream.