Peel and finely dice the apples. Toss them with dark brown sugar, cinnamon, salt, and lemon juice until combined, then cook over low-medium heat for about 10 minutes until caramelized. Chill in the fridge.

Melt the butter in a pot over medium heat, stirring until golden brown with milk solids floating. Cool in the fridge for 10 minutes.

In a bowl, whisk flour, baking soda, cream of tartar, cinnamon, salt, and cornstarch together and set aside.

Whisk cooled brown butter, dark brown sugar, granulated sugar, and vanilla until combined. Add egg and yolk, whisking until smooth, then fold in cooled caramelized apples.

Fold dry ingredients into wet ingredients until a dough forms. Cover tightly and chill for 2-3 hours.

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

Use a cookie scoop to form balls of dough, rolling them in the cinnamon sugar mixture until coated. Place cookies 2-3 inches apart on the baking sheet.

Bake for 12-14 minutes until edges are set and golden brown, letting cookies cool on the baking sheet for 5 minutes before transferring to a rack.