Preheat the oven to 350°F (175°C).

In a mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until smooth.

Beat in the eggs one at a time, mixing well after each addition.

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

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

Fold in the diced apples.

In a small bowl, mix together the granulated sugar and ground cinnamon for the coating.

Scoop tablespoon-sized portions of dough and roll them into balls.

Roll each ball in the cinnamon sugar mixture until fully coated.

Place the coated dough balls on a baking sheet lined with parchment paper, spacing them about 2 inches apart.

Bake in the preheated oven for 8-10 minutes, or until the edges are lightly golden.

Remove from the oven and let cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.