In a large bowl, mix together the sourdough starter, milk, and yogurt until smooth.
Add the baking powder and flour and stir to combine to a shaggy, somewhat sticky dough.
Cover the bowl with a damp cloth and let the dough rise in a warm place for 2-3 hours.
After the dough has raised, dump out the dough onto a lightly floured counter and knead for a minute or two, until smooth. You shouldn't need to add much extra flour, if any, to make it not stick to your hands.
Preheat a heavy cast-iron skillet over medium-high heat.
Divide the dough into 8 pieces and roll each piece into about 1/4" thickness.
Brush one side with melted butter and place butter-side down on the skillet.
Cook for about a minute, or until the dough starts to bubble and release from the skillet.
Brush the other side with melted butter and flip.
Cook for an additional minute.
Transfer to a plate and cover with a cloth to keep warm.
Repeat with remaining pieces of dough and Enjoy!