Peel and finely dice the apples. Toss them together with the dark brown sugar, cinnamon, salt, and lemon juice until combined. Heat the apples on the stove and cook them down until browned and caramelized, about 10 minutes over low-medium heat. Set aside in the fridge to chill.

Melt the butter in a pot over medium heat. Stir occasionally until the butter stops bubbling and begins to brown. Remove from heat and pour into a different container. Cool in the fridge for 10 minutes.

Whisk together the flour, baking soda, cream of tartar, cinnamon, salt, and cornstarch. Set aside.

In a separate bowl, whisk together the cooled brown butter, dark brown sugar, granulated sugar, and vanilla until combined. Add the egg and egg yolk, whisk until smooth. Gently fold in the cooled caramelized apples until evenly incorporated.

Add the dry ingredients to the wet ingredients and gently fold until a dough forms. Tightly cover and chill the dough for 2-3 hours.

Preheat the oven to 350?F and line a baking sheet with parchment paper. In a small bowl, whisk together the granulated sugar and ground cinnamon for the coating.

Use a cookie scoop to roll the dough in the cinnamon sugar until generously coated. Space the cookies 2-3 inches apart on the baking sheet.

Bake for 12-14 minutes until the edges are set and golden brown but the tops are puffy and slightly underdone. Let cool on the baking sheet for 5 minutes before transferring to a cooling rack to cool completely or enjoy slightly warm!