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

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

In a large mixing bowl, beat the softened butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes.

Add the egg and vanilla extract, beating until well combined and smooth, about 1-2 minutes.

Gradually add the dry ingredients to the wet ingredients, mixing on low until integrated.

Gently fold in the finely chopped apples using a spatula until evenly distributed.

Mix granulated sugar and ground cinnamon in a small bowl for rolling.

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

Place the coated dough balls on the prepared baking sheet, spacing them 2 inches apart. Bake for 10-12 minutes until edges are golden brown.

Let the cookies sit for a few minutes before transferring to a wire rack to cool completely.