Preheat oven to 350˚ Fahrenheit with the rack in the middle. Melt the butter in the oven in a 10 inch cast iron skillet. Remove from the oven when it's melted.
Whisk together the dry ingredients in a large bowl: the flour, baking powder, cinnamon and salt. In another bowl combine the milk, vanilla, lemon juice and 1 cup of the brown sugar. Pour the wet ingredients into the dry and mix until smooth. Toss the blueberries with 1 tbsp of brown sugar. Pour the batter into the buttered skillet. Top with the blueberries.
Bake for 30 minutes. Let cool a few minutes then serve with vanilla ice cream or whipped cream.