The evening before, whisk together your flour, sugar, cinnamon, salt and baking powder in a medium sized bowl. Add in your milk, butter and starter, using the whisk again to combine everything until smooth.
Cover and let sit on the counter overnight to ferment and let flavour develop!
The next day before you are ready to bake, add in your egg and lemon zest to the batter. I like the whisk my egg and lemon zest together with a fork before adding to the batter to make mixing easier. Place the batter aside.
In a 10" cast iron pan, add in a tablespoon of butter and let melt on a medium heat. Pour your frozen blueberries into the pan and let this heat for about 5-10 minutes or until the blueberries are quite thawed and soft. Stir every minute or so. Turn the heat off.
Preheat your oven to 350 degrees.
Pour your batter over the blueberries into the cast iron pan. Use a small spoon to stir the batter GENTLY until you get some pretty blue swirls thru the top. Do not mix, just gently stir the batter! We want the blueberries to sit on the bottom of the pan mostly.
This is optional, but we love some sprinkles of sugar on top before the bake!
Bake for 15-18 minutes or until it passes the knife test.
Straight out of the oven, feel free to sprinkle a little more sugar on top and add some lemon zest too! Serve alone or with cream or, our favorite, whipping cream.
Keeps 7 days in the fridge and can be eaten cold or reheated.