Gradually add the dry ingredients into the wet mixture, stirring gently just until a smooth, pourable batter forms. The word "gently" here is important — avoid overmixing the batter once the flour goes in, as too much stirring develops the gluten in the flour and will make the finished pie tough and dense rather than soft and tender.
Fold the prepared apple slices into the batter, turning them gently until they are evenly coated from all sides. Pour the entire mixture into your prepared baking dish and spread it out evenly across the surface with the back of a spoon or a spatula so everything bakes uniformly.
Place the dish in the preheated oven and bake for approximately 30 to 35 minutes, or until the top of the pie is a deep, even golden color and a toothpick or thin knife inserted into the very center of the pie comes out completely clean with no wet batter clinging to it. Allow the pie to cool in the dish for at least 10 minutes before slicing and serving — this resting time lets the interior set properly and makes the pie far easier to cut into neat portions.
