Salted Caramel Apple Hand Pies

Name: Salted Caramel-Apple Hand Pies
Ingredients: 2 Granny Smith apples, peeled and cut into small cubes (2 cups); .25 cup granulated sugar; 2 teaspoons all-purpose flour, plus more for work surface; 2 teaspoons fresh lemon juice (from 1 lemon); .5 teaspoon ground cinnamon; .25 teaspoon kosher salt; 2 (14.1-oz.) pkg. refrigerated piecrusts (4 piecrusts total); 8 soft caramel candies, roughly chopped; Pinch of flaky sea salt; 1 large egg; Sanding sugar (optional)