1. Whisk together the flour, salt and baking powder in a large bowl. Add the cubed butter to the bowl and use your fingers to work the butter into the flour until the mixture is the consistency of wet sand. Stir in the sour cream (the dough will be very wet), and then turn the dough out onto a well-floured work surface.
2. Knead the dough a few times until it comes together, adding more flour, 1 teaspoon at a time, if the dough is too sticky to handle. Wrap it securely in plastic wrap and refrigerate it for at least 30 minutes while you make the filling.
3. In a medium bowl, mix apples, lemon juice, flour, sugar, and cinnamon. Set aside.
4. Preheat the oven to 425ºF.
5. Remove the dough from the refrigerator and rolling it out onto a well-floured surface. Using a 3-inch circular cookie cutter or cup, cut out as many circles as possible. Re-roll the scraps and continue cutting out circles until you run out of dough, ensuring you end up with an even number of circles. (You should have approximately 18 3-inch circles.)
6. Place half of the crusts on the parchment paper-lined cookie sheet. Top each pie crust circle with about a tablespoon of the apple mixture. Cover with a few pieces of caramel. (Sprinkle with sea salt if you using a store bought caramel)
7. Place a second dough circle atop each filled circle then use a fork to crimp the edges together, sealing each pie. Using a sharp knife, cut two or three vents on the top of each pie. Brush each pie with the egg wash using a pastry brush.
8. Bake in pre-heated oven for around 15 minutes, or until pies are golden brown. Allow to cool on a cooling rack. Keep in an airtight container and enjoy!