Preheat oven to 400 degrees.
To make the dough, mix the flour, sugar, baking powder, salt, and cinnamon in a large mixing bowl. Cut in the butter using a pastry cutter or two butter knives until you have a coarse, crumbly mixture. Pour in the boiling water and stir to combine. Set aside.
To make the filling, dissolve the cornstarch in the water. Add the berries to a large, deep cast iron skillet over medium heat. Add the cornstarch slurry, lemon juice, and sugar to the pan and stir well.
Heat mixture over medium heat until boiling, stirring frequently. Remove from heat.
Drop small pieces of dough evenly over the berry mixture. Place the cast iron pan on a foil lined cookie sheet and place in the oven. Bake for 20-25 minutes, until the dough is golden brown and the berries are thick and bubbly.
Serve warm with vanilla ice cream, if desired.