This recipe is all about building layers of fall flavor. You get a deep, nutty taste from brown butter, which works so well with tart apples that get cooked down until they're nicely caramelized. All of that gets folded into a chewy snickerdoodle dough. You really can't skip the chill time here; it's what helps the flavors meld and keeps the cookies from spreading into thin crisps in the oven.
Combine diced apples, brown sugar, cinnamon, salt, and lemon juice in saucepan. Cook over low-medium heat 10 minutes until jammy. Refrigerate until cool.
Brown butter over medium heat until golden and nutty, about 5-7 minutes. Transfer to bowl and refrigerate 10 minutes.
Whisk flour, baking soda, cream of tartar, cinnamon, salt, and cornstarch in medium bowl.
Mix cooled brown butter, sugars, and vanilla in large bowl. Whisk in egg and yolk until smooth.
Fold in cooled apples, then dry ingredients until just combined.
Chill dough 2-3 hours.
Preheat oven to 350F. Line baking sheet with parchment.
Mix granulated sugar and cinnamon for coating.
Scoop 2 tablespoon portions, roll into balls, coat in cinnamon sugar.
Place on baking sheet 3 inches apart.
Bake 12-14 minutes until edges are set but centers slightly puffy.
Cool on baking sheet 5 minutes, then transfer to wire rack.
Notes
Cookies will continue setting while cooling. Dough must be thoroughly chilled for best results.