Combine diced apples, sugar, cinnamon, lemon juice, and cornstarch in a medium saucepan. Cook over medium heat for 8-10 minutes, stirring occasionally, until apples soften slightly and liquid thickens. Remove from heat and cool completely - warm filling will make the dough soggy.

Preheat oven to 375 degrees F. Unroll pie crust on a lightly floured surface. Using a 3-inch round cutter, cut out 12 circles, rerolling scraps once if needed.

Place 6 circles on a parchment-lined baking sheet. Spoon 1 heaping tablespoon of cooled filling onto each, leaving a 0.5-inch border. Brush edges with egg wash, top with remaining circles, and press firmly to seal. Crimp edges with a fork to prevent leaking.

Cut 2 small slits in each pie top for steam to escape. Brush tops with remaining egg wash and sprinkle with coarse sugar. Bake 22-25 minutes until deep golden brown. Cool on the pan 10 minutes before serving.