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

In a mixing bowl, whisk together the flour, cream of tartar, baking soda, and salt. Set aside.

In a separate bowl, beat together the softened butter, granulated sugar, and brown sugar until light and fluffy. Add the eggs, one at a time, mixing well, then add the vanilla.

Gradually add the dry ingredients to the wet mixture, folding in the diced apples carefully.

Using a cookie scoop, portion out the dough into balls and chill in the refrigerator for 20-30 minutes.

Prepare the cinnamon sugar coating by mixing sugar, cinnamon, and nutmeg. Roll the chilled dough balls in this mixture.

Place the dough balls on the baking sheet, leaving space between them, and bake for 8-10 minutes until slightly underdone.

Let the cookies rest on the tray for 2-3 minutes before transferring them to a wire rack to cool.