Preheat oven to 475°F with the 10′ Cast Iron Skillet inside.
Beat the eggs and mix in the flour and sourdough starter. Heat the milk separately and mix with the egg and flour mixture. Add sugar, salt, and vanilla and mix well. Batter should be runny.
Once the oven is fully preheated and the skillet is hot, add the butter to the pan. Allow it to melt and gently tilt the pan to coat it. (this will not take long, at this point you should move fairly quickly to avoid burning the butter)
Add the batter to your pan and bake for ~12 minutes. The pancake should have ‘poofed’ up the sides, and appear fluffy, with browning around the edges.
Remove from the oven and top with lemon juice and powdered sugar to taste. (Note, less lemon juice will be required than for a standard dutch baby - take care not to over-sour your breakfast)