Preheat cast iron skillets and melt butter in them.
Mix together sourdough starter, eggs, milk, and salt.
Add melted butter and mix until smooth.
Pour crepe batter into hot skillets, about half a cup per skillet, and use spatula to spread out batter into a thin pancake.
Allow to cook until almost completely cooked through, and then flip. This will help them not break.
Allow to cook for 1-2 more minutes and then place on a plate.
To make the filling, mix together room temperature cream cheese with maple syrup and vanilla until smooth.
Whip heavy cream until stiff peaks form, then fold in with the cream cheese mixture.
Notes
Preheating is a must; the crepes will stick to your cast iron skillet if the pan is cold.
Also, make them thin so they don't stick. I will add about a 1/2 cup of the crepe batter to the cast iron skillet, then use a spatula to spread out the mixture thinly and evenly.
Make sure the crepe is just about fully cooked before you flip it. If you flip it early, it will break. I usually get four cast iron skillets going to make the crepe-making process super fast.