Add finely chopped apples to a skillet with brown sugar, lemon juice and a teaspoon of cinnamon. Heat over medium heat until they have softened and there is no more liquid. Remove to a bowl and refrigerate until cooled.
You can use softened butter or brown the butter for more flavor. If you want to brown the butter, use a light colored saucepan and heat the butter over medium-high heat until it starts to turn brown. Immediately remove to a glass bowl and refrigerate until is firm but soft.
Preheat the oven to 375º and line baking sheets with parchment paper.
In a large bowl, whisk the flour, cream of tartar, baking soda, cornstarch and salt.
In the bowl of a stand mixer, combine softened butter, and sugar and beat on medium high until light and fluffy, about 3 minutes.
Add eggs, one at a time and mix well after each addition. Turn speed to low and gradually add flour until well combined. Gently mix in cooled apples.
In a small bowl combine cinnamon and sugar.
Use an ice cream scoop to scoop out dough and use your hands to roll into balls. Place each ball in the bowl of cinnamon sugar mixture and coat completely. Place on the prepared baking sheet at least 2 inches apart.
Bake for 10 minutes until the edges are slightly brown and the center is still soft. Allow to cool on the pan for 10 minutes and then remove to a rack to cool completely.