Preheat your oven to 350℉.
In your mixing bowl, combine the granulated sugar and lemon zest. Work these together with your hands until fragrant - this infuses the sugar with the lemon zest.
To the same mixing bowl with the lemon sugar, add the flour, light brown sugar, salt, baking powder and whisk together until combined.
To the flour mixture, add the milk, vanilla extract, and lemon juice - whisk to until smooth.
In a separate mixing bowl, combine the blueberries with 1 tablespoon granulated sugar.
Once your oven is preheated to 350℉ place the 6 tablespoon of butter in your cast iron skillet and place the skillet into the oven to melt the butter.
Once the butter is melted, take the skillet out of the oven, pour in the batter, smooth it to the edges.
Top with the blueberries and sprinkle the remaining 2 tablespoon granulated sugar evenly over the top.
Bake for 40-45 minutes until golden brown.