Pre-step: preheat the oven to 400 degrees.

Make the apple pie filling:

1. Heat the 2 tbsp. butter over medium heat in a large skillet. Once melted, add the peeled, sliced apples, brown sugar, cinnamon and pinch salt. Cook for 3 - 4 minutes, stirring frequently, or until the brown sugar is fully dissolved and the apples have released some moisture.
2. Sprinkle 1 tbsp. of flour over the top of the apples and stir to evenly combine the flour with the apple filling. Cook, stirring frequently, for an additional 1 - 2 minutes, or until the apple pie filling has thickened. Turn the heat down if necessary to avoid the sugar burning.
3. If the filling is still watery, add up to an additional 1 tbsp. of flour and cook for an additional minute, stirring frequently. (Mine took about 1 and 3/4 tbsp. to properly thicken - for a visual reference of what the thickness of filling should look like, see the photo in the blog post.)
4. Turn the heat off and set the pan aside.

Make the crust batter:

1. Add the 10 tbsp. of softened butter, 2 tbsp. brown sugar and 2 tbsp. granulated sugar to a large bowl or the bowl of a stand mixer. Beat with hand beaters or the whip attachment of a stand mixer on medium speed until evenly combined and slightly fluffy, about 1 minute.
2. Add the egg and beat again until the mixture is smooth, about 30 seconds.
3. Add the flour, baking powder and salt. Beat on low speed just for a few seconds to moisten the flour, then on medium speed until the flour is fully combined and the mixture is smooth, about 1 minute. 
4. While continuing to beat the mixture on medium speed, drizzle the water slowly into the batter and mix until smooth, about 1 minute.

Assemble and bake:

1. Pour the batter into a greased 9 inch pie dish, making sure to spread the filling all the way out to the edges. Carefully spoon the apple pie filling into the center of the batter. If the fruit is mounded, gently smooth out the top, but do not stir. Leave 1 inch of batter around the edge of the dish (this is what will form the crust).
2. Bake in the preheated oven for 35 - 40 minutes, or until the crust is deep golden brown (see note).