Preheat your oven to 350°F (175°C).

In a medium bowl, whisk together flour, baking powder, cinnamon, and salt.

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

Add the egg and vanilla extract to the butter mixture and mix until well combined.

Gradually add the dry ingredients to the wet mixture, mixing until just combined.

In another bowl, combine the diced apples, lemon juice, brown sugar, nutmeg, and a pinch of salt.

Fold the apple mixture into the cookie dough gently.

Drop spoonfuls of the combined dough onto a baking sheet lined with parchment paper.

Bake for 12-15 minutes, or until the edges are lightly golden.

Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack.