In a 10-inch cast iron skillet or deep saucepan, combine the sliced peaches, blueberries, 1/2 cup of the sugar, water, and lemon juice.

Place the skillet over medium-high heat and bring the mixture to a gentle boil, stirring occasionally until the sugar has dissolved and the fruit begins to release its juices.

While the fruit heats, prepare the dumpling dough by whisking together the flour, the remaining 1/4 cup sugar, baking powder, salt, and cinnamon in a medium mixing bowl.

Pour the melted butter and milk into the dry ingredients, stirring gently until a soft, sticky dough forms; be careful not to overmix or the dumplings will become tough.

Once the fruit mixture is bubbling steadily, reduce the heat to low and drop rounded tablespoons of the dough evenly over the surface of the fruit.

Cover the skillet tightly with a lid or aluminum foil and let it simmer undisturbed for 15 to 20 minutes.

Cook until the dumplings are puffed and cooked through, which you can test by inserting a toothpick into the center of a dumpling to ensure it comes out clean.

Remove the skillet from the heat and let it cool for 5 minutes before serving warm with a scoop of vanilla ice cream.