Preheat your oven to 350°F (175°C) and gather all your ingredients and tools.

In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until smooth and fluffy, about 2-3 minutes.

Beat in eggs one at a time, incorporating each fully before adding the next, then add the vanilla extract.

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

Gradually add the dry mixture to the butter-sugar mix. Stir until just combined.

Fold in the diced apples gently to incorporate.

Mix the sugar and cinnamon for rolling in a small bowl.

Scoop out tablespoon-sized portions of dough, roll into balls, then coat in cinnamon sugar.

Place coated cookie balls on lined baking sheets, leaving 2 inches of space between them.

Bake for 10-12 minutes until edges are golden and centers are soft.

Allow cookies to cool on the baking sheet for a few minutes before transferring to a wire rack.