Found this on FB.  No real source.

~APPLE PIE BAKED IN APPLE~

5-6 Granny Smith apples (make sure they can stand on their own)
1 tbsp. cinnamon
1/4 cup sugar
1 tbsp. brown sugar
pie crust (homemade or pre-made)

1) Preheat oven to 375F.

2) Cut off the top of 4 apples off and discard. Remove the inside of each apple with a spoon or melon baller very carefully, as to not puncture the peel.

If you’re a skilled interior apple excavator, salvage as much as you can so you can use it for Step 2. I, on the other hand, am not skilled so I just had to throw my interior apples away and chop up additional apples for filling.  (or just rinse them and eat them)

3) Remove skin from remaining apple(s) and slice very thinly. These apple pieces will give you the additional filling needed to fill the four apples you are baking.

Mix sliced apples with sugars and cinnamon in a bowl. If you prefer more or less cinnamon make adjustments as desired. Same goes for the sugar.

Scoop sliced apples into hollow apples.

4) Roll out pie crust and slice into 1/4 inch strips. You can also add a strip of pastry inside the top of the apple almost like a liner to add a little more texture/sweetness to the pie.

Cover the top of the apple in a lattice pattern with pie crust strips.

5) Place apples in an 8×8 pan. Add just enough water to the cover the bottom of the pan.

Cover with foil and bake for 20-25 minutes.

Remove foil and bake for an additional 20 minutes or until crust is golden brown and sliced apples are soft.

Makes 4 baked apple pies (in the apple).