In a medium bowl, combine the diced apples, brown sugar, cinnamon, lemon juice, and cornstarch. Toss until well-coated. Let this mixture sit while making the dough.

In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add in the egg and vanilla extract, mixing until combined.

In another bowl, whisk together the flour, baking powder, and salt. Gradually add this dry mixture into the wet ingredients, blending until it forms a dough.

Preheat your oven to 350°F (175°C) and prepare your baking sheet with parchment paper.

Scoop out a tablespoon of dough, flatten it slightly, and place a spoonful of the apple filling in the center. Fold the dough over the filling and seal it well. Place on the baking sheet and repeat.

Bake in the preheated oven for about 15-20 minutes, or until the edges are lightly golden.

Once cool, dust your cookies with powdered sugar and serve warm. Optionally, add a scoop of vanilla ice cream on top.