Preheat oven to 425 degrees. Grease a 12-cup muffin tin thoroughly and set aside.
Peel core and chop apples into small pieces and toss with some lemon juice. Set aside.
Combine sugars, cornstarch, cinnamon, nutmeg and salt in a small saucepan. Pour in water and stir until incorporated. On medium heat, bring mixture to a gentle boil for 3 minutes stirring frequently to prevent scorching on the bottom. Once mixture is thickened slightly, add apples and toss bringing he mixture to a gentle boil once again. Reduce the head to low and simmer for 10 minutes or until the apples are tender. Take mixture off heat and allow it to cool slightly.
While mixture is cooling, thaw pie crusts if needed and unroll one crust onto a flat surface. Start by cutting 3 1/2 - 4" circles with a cookie cutter or rim of a glass/bowl. Place each disk into each muffin tin cavity, pressing them into the bottom and up the sides. Fill with apple pie filling about 2/3 to the top.
With the second pie crust, unroll and cut into 1/2" strips. Cut the long strips into 2 1/2" smaller strips. On a flat surface, place three strips vertically and three strips horizontally, creating a lattice pattern. Press down slightly with the palm of your hand so that they stick together. Refer to the picture in the post for a visual. (You can skip this step all together and just create the lattice pattern the traditional way and place them individually on top of the mini pies. Alternately, you can even just skip the lattice all together and just cut out a bunch of circles, place them on top and cut vent holes in the tops.)
Transfer lattice crust to the muffin tins and place on top of the apple pie filling. Press down slightly around the edges and trim away the excess with a sharp knife.
Brush the tops of the apple pies with egg wash, sprinkle them with some sugar and bake for 15-17 minutes or until tops are lightly golden and cooked through.
Mini apple pies are best served the same day made but will keep for up to 2 days stored in an airtight container.