whisk together the flour, baking powder and salt. work in the butter until pea-sized. stir together the yogurt and milk and add it to the flour mixture, stir until dough forms. on a lightly floured surface flatten into a rectangle fold like a business letter, repeat 3-4 times. on the last turn roll out and cut out your biscuits. brush with milk. bake at 425F for about 15 minutes in a cast iron skillet.