Preheat your oven to 350°F (175°C) and prepare your baking sheets by lining them with parchment paper or silicone mats.

In a medium bowl, whisk together the all-purpose flour, cream of tartar, baking soda, and salt until well combined.

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

Incorporate the eggs into the butter-sugar mixture, one at a time, mixing well after each addition. Then, add the vanilla extract.

Gradually add the dry ingredient mixture into the wet ingredients, mixing on low speed until incorporated, then fold in the diced apples.

Scoop out the dough into balls about 1½ tablespoons each, place on a tray, and chill in the refrigerator for 20-30 minutes.

Combine the granulated sugar and ground cinnamon in a small bowl for the coating.

Roll each chilled dough ball in the cinnamon-sugar mixture until fully coated and place them back on the tray.

Bake the cookies for 8-10 minutes until slightly underdone in the center but set around the edges.

Let the cookies rest on the baking sheets for 2-3 minutes before transferring them to a cooling rack.