In a deep skillet or Dutch oven, combine the blueberries, sugar, cinnamon (if using), water, and lemon juice. Bring to a gentle boil over medium heat. Simmer for about 10 minutes, until the berries soften and release a syrupy sauce.

In a separate bowl, whisk together the flour, baking powder, salt, and sugar. Cut in the cold butter using a pastry cutter or your fingertips until the mixture becomes crumbly. Stir in the milk just until combined—avoid overmixing to keep the dumplings light and fluffy.

Drop spoonfuls of the dumpling dough over the simmering blueberry mixture. Space them slightly apart to allow room for steaming.

Reduce the heat to low and cover the pan tightly with a lid. Steam the dumplings for 15 minutes without lifting the lid. The dumplings will cook in the steam and become tender and fluffy.

Spoon the dumplings and berries into bowls while hot. For an extra treat, top with whipped cream or a scoop of vanilla ice cream.