01 - Preheat oven to 350°F. Generously grease a 10-inch ovenproof skillet, preferably cast iron, with butter or nonstick spray.
02 - In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, and ground cinnamon. Set aside.
03 - In a large bowl, whisk melted butter and granulated sugar until smooth. Add eggs one at a time, whisking after each addition. Stir in vanilla extract and Greek yogurt or sour cream until homogeneous.
04 - Gradually fold the dry mixture into the wet ingredients, mixing gently until just combined. Avoid overmixing to maintain a tender crumb.
05 - Gently fold in diced apples and cranberries until evenly distributed throughout the batter.
06 - Spread batter evenly into the prepared skillet. If desired, mix coarse sugar and extra ground cinnamon, then sprinkle evenly on top for added texture.
07 - Bake at 350°F for 38 to 42 minutes, or until the surface is golden and a toothpick inserted in the center comes out clean.
08 - Allow to cool in the skillet for at least 15 minutes before slicing. Serve warm or at room temperature.