Mix together the sourdough starter discard, milk, and sour cream in a large bowl. Mix until smooth and combined.
In a separate bowl, stir together the flour, baking powder, and salt. Add the dry ingredients into the liquid mixture, and mix until the dough forms a ball. Add additional flour if the dough is too sticky. Gently knead the dough just until smooth. Grease the bowl, and cover the bowl with a towel.
Set in a warm place and let the dough rise for approximately 3-4 hours. Once dough has risen slightly, knead again gently on a lightly floured surface. Divide the dough into 8-10 dough balls.
Roll the dough balls into thin circles that are approximately ¼ inch (or thinner). Try to use the minimal amount of flour while rolling them out.
Heat a cast iron skillet over medium heat. Melt a thin layer of butter in the cast iron pan (about 1 tsp). Place the dough in the hot cast iron skillet. Cook for about 1 minute or until the dough is nice and bubbly. Turn the dough and cook the other side until cooked through, for approximately another minute. Allow to cool on a cooling rack.