In a large bowl, combine sourdough starter, flour, and milk. Cover the bowl with a towel or cloth and leave at room temperature overnight (up to 24 hrs). Take one cup and return it to the fridge for use later.
Whisk eggs, baking soda, salt, cinnamon, and sugar into the fermented flour and milk mixture.
Preheat oven to 450 degrees. With cast iron inside of the oven.
Once the skillet is hot, remove it and put on a safe work surface.
Add one tablespoon of butter and let it melt and coat the bottom of the skillet.
Add in a single layer of fruit and give it a second to sizzle. Put over heat if your pan has cooled too much.
Add in the batter. You want to add in enough batter to cover the fruit and the bottom of your skillet.
Place the skillet back in the over for approximately 15 minutes, or until the pancake looks evenly cooked and the edges have a bit of crisp to them.
Repeat with remaining batter.
Serve with favorite condiments, syrups, fruit, or Chantilly cream.
