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

In a medium bowl, whisk together the all-purpose flour, baking soda, cream of tartar, ground cinnamon, ground nutmeg, and salt.

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

Add the egg and vanilla extract to the butter mixture, then mix in the dry ingredients until just combined.

Gently fold in the finely chopped apple pieces using a spatula.

Roll the dough into 1-inch balls and coat each ball in the cinnamon-sugar mixture.

Place the dough balls on the baking sheet, spaced about 2 inches apart. Bake for 10-12 minutes.

Let the cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.