Preheat your oven to 375°F. Line your baking sheets with parchment paper. This saves cleanup later, which matters when the sink is already full.
In a medium bowl, whisk together the flour, cream of tartar, baking soda, salt, and cinnamon. Set it aside. This is the calm moment before the mess.
In a large bowl, beat the butter and sugar together until light and fluffy. This usually takes about two minutes. Do not rush this part. It helps keep the cookies soft.
Add the eggs one at a time, mixing well after each one. Stir in the vanilla. The dough should look smooth and slightly thick.
Slowly add the dry ingredients into the wet mixture. Mix just until everything comes together. Overmixing makes cookies tough and nobody wants that.
Gently fold in the chopped apples. Make sure the pieces are small. Big chunks make the cookies fall apart and that is annoying.
In a small bowl, mix the sugar and cinnamon for the coating. This step smells amazing already.
Scoop the dough into balls, about one and a half tablespoons each. Roll each ball in the cinnamon sugar and place them on the baking sheet with space in between.
Bake for 10 to 12 minutes. The edges should look set, but the centers should still look soft. They will firm up as they cool.
Let the cookies cool on the baking sheet for about five minutes, then move them to a cooling rack. Or eat one warm like we always do.