While apples are softening, whisk together flour, sugar, baking powder, cinnamon, and salt.
In a separate bowl, whisk melted butter, milk, vanilla and egg. Whisk mixture into dry ingredients just until combined, then pour batter into prepared pan.
Scoop topping evenly over the batter and bake until edges are golden and tester comes out clean from the center, 22-24 minutes.
Serve warm, with whipping cream, syrup, ice cream, or a dusting of icing sugar - or just as is, it's delicious any way!
Notes
For a quick and easy topping, skip the apple mixture and simply sprinkle a cup of your favourite fresh or frozen berries over the batter before baking.
Recipe by Hidden Ponies at https://hiddenponies.com/2014/09/one-dish-oven-baked-apple-crumble-pancake/