Combine the blueberries, 100 g sugar, water, lemon juice, and cinnamon in a 26 cm / 10-inch pot with a tight-fitting lid. Bring to a simmer over medium heat, stirring occasionally.

Simmer uncovered for 8 to 10 minutes, until the berries have broken down and the liquid looks glossy and syrupy, coating the back of a spoon.

While the fruit simmers, whisk the flour, baking powder, salt, and 2 tbsp sugar together in a mixing bowl.

Cut the cold butter into the flour with your fingertips or a pastry cutter until the mixture looks like coarse crumbs.

Pour in the milk and stir with a fork just until a soft, sticky dough comes together. Stop as soon as no dry flour remains, overmixing makes the dumplings tough.

Drop the dough by heaping tablespoons directly onto the surface of the simmering blueberries, spacing them apart. You'll get about 8 dumplings.

Cover the pot tightly and reduce the heat to low. Steam for 15 to 18 minutes without lifting the lid, or the dumplings will turn gummy on top.

Check doneness with a toothpick inserted into the center of a dumpling, it should come out clean with no wet dough.

Remove from the heat and let sit, covered, for 5 minutes.

Spoon the warm blueberries and dumplings into bowls and serve with heavy cream or a scoop of vanilla ice cream.