Creating these irresistible mini apple pies is straightforward when you follow these steps:

1. Prepare the Crust: In a bowl, mix together flour, salt, and sugar. Cut in butter until the mixture resembles coarse crumbs. Stir in water, a tablespoon at a time, until the mixture forms a ball. Wrap in plastic wrap and refrigerate for at least 30 minutes.

2. Preheat the Oven: Preheat your oven to 425°F (220°C).

3. Make the Filling: In a large bowl, combine sliced apples, sugar, cinnamon, nutmeg, lemon juice, and cornstarch. Toss until the apples are well coated.

4. Roll Out Dough: On a lightly floured surface, roll out the dough to about ⅛ inch thick. Cut rounds using a 4-inch biscuit cutter or a similar object.

5. Assemble the Pies: Place the rounds into greased muffin tins. Press gently to fit. Spoon the apple mixture into each crust, filling them generously.

6. Create Tops: Roll out more dough to cut out small circles or shapes for the tops. Place them over the apple filling, sealing the edges by pinching together or pressing with a fork.

7. Prepare Egg Wash: In a small bowl, mix the egg and milk. Brush the tops of the pies with the egg wash for a golden finish.

8. Bake: Bake in the preheated oven for 20-25 minutes, or until the crust is golden brown and the filling is bubbling.

9. Cool: Remove from the oven and let the pies cool in the tins for 10 minutes. Then, transfer them to a wire rack to cool completely.

10. Enjoy: Once cool, these mini apple pies are ready to be devoured!