Peel, core, and chop the apples into small chunks.

In a large skillet, melt the 3 tablespoons of butter over medium heat. Add the chopped apples and sauté for 5 minutes until softened.

Add 1/4 cup dark brown sugar, 3 tablespoons granulated sugar, 1 1/2 tablespoons lemon juice, 1 teaspoon cinnamon, and 1/4 teaspoon salt to the pan. Stir to combine, cooking for an additional 5-7 minutes until the apples are tender and the sugar has melted into a syrupy mixture.

Remove the pan from the heat and let the filling cool completely.

Preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper.

Roll out the thawed puff pastry on a lightly floured surface. Cut the pastry into 8 equal squares or rectangles (depending on your preference).

Spoon about 2-3 tablespoons of the cooled apple filling into the center of each pastry square, being careful not to overfill.

Fold each pastry square into a triangle, enclosing the apple filling inside.

Press the edges together with a fork to seal the turnovers. Use a sharp knife to make a small slit on top of each turnover to allow steam to escape during baking.

In a small bowl, whisk together the egg, egg yolk, 2 teaspoons milk, and pinch of salt.

Brush the egg wash generously over the tops of the turnovers.

Sprinkle 3 tablespoons granulated sugar on top for extra sweetness and crunch.

Place the turnovers on the prepared baking sheet and bake in the preheated oven for 20-25 minutes, or until golden brown and puffed up.

Remove from the oven and let the turnovers cool on a wire rack.

In a small bowl, whisk together 3/4 cup confectioners' sugar and 1 tablespoon milk until smooth.

Drizzle the glaze over the cooled turnovers before serving.