Caramelize the Apples: Peel and finely dice Gala apples, toss with sugar, cinnamon, salt, and lemon juice in a medium skillet. Cook over medium heat for about 10 minutes until tender and caramelized.

Brown the Butter: In a saucepan, melt unsalted butter over medium heat, stirring until golden brown, approximately 5-7 minutes. Cool in the fridge for about 10 minutes to solidify slightly.

Whisk Dry Ingredients: In a large mixing bowl, combine flour, baking soda, cream of tartar, salt, cornstarch, and ground cinnamon. Whisk to blend thoroughly without lumps.

Combine Wet Ingredients: Mix cooled brown butter with dark brown sugar and granulated sugar until smooth. Add vanilla, whole egg, and egg yolk until fully combined. Fold in caramelized apple mixture.

Form the Dough: Gradually add dry mixture to wet mixture, folding gently. Cover with plastic wrap and chill in the refrigerator for 2-3 hours.

Bake the Cookies: Preheat oven to 350°F (175°C). Scoop tablespoons of chilled dough, roll in cinnamon-sugar mix, and place on a baking sheet. Bake for 12-14 minutes until golden.

Cool and Serve: Let cookies cool on baking sheet for about 5 minutes, then transfer to a wire rack to cool completely.