Place a 9" cast iron skillet in the oven and preheat the oven to 475 degrees℉ for 15-30 minutes.
While the oven is preheating, measure out and mix up the sourdough starter, milk, eggs, maple syrup, and salt in a large mixing bowl. Make sure the eggs are completely incorporated into the mixture. Let the mixture rest while the pan is heating up.
When thoroughly heated, carefully remove the hot cast iron and add 1/2 stick of butter, swirling it around the pan as it melts.
When fully melted, add the Dutch baby batter into the pan and quickly put the cast iron back into the oven to bake for 20-30 minutes or until it's golden brown on top and the sides of the pancake have pulled away from the cast iron skillet.
Remove from oven and let it cool slightly before cutting and serving with a drizzle of maple syrup and a hot cup of joe!
Bon Appétite!