*To make this skillet into snickerdoodle cookies, see the recipe notes below.
Prep: Preheat the oven to 350°F. Spread the softened butter all over the bottoms and sides of a 10-inch skillet. Set aside.
1-2 Tbsp. softened butter
Brown the butter: For a detailed tutorial, see this post on how to brown butter. Allow the butter to cool slightly, ~10-15 minutes. Start Timer 1 cup unsalted butter
Combine sugars: Add the sugars to the cooled browned butter and whisk until combined. Some of the mixture may get stuck in the whisk; just give it a tap to get it all out.
1 cup granulated sugar, 3/4 cup dark brown sugar
Add wet ingredients: Add the egg, egg yolk, milk, and vanilla extract. Whisk to combine until smooth. Be sure to break up any large clumps of brown sugar if you find any.
1 large egg + 1 egg yolk, 2 Tbsp. whole milk, 1 Tbsp. vanilla extract
Fold in dry ingredients: Add in the dry ingredients and fold just until combined. The cookie dough will be thick!
2 2/3 cups all-purpose flour, 2 tsp. cream of tartar, 1 tsp. kosher salt, 1 tsp. baking soda
Press into pan: Turn the cookie dough out into the prepared pan. Press the cookie down into an even layer.
Add topping: Combine the cinnamon and sugar topping together and sprinkle some over the tops. You don't have to use all of it; you can reserve some for serving.
1 Tbsp. sugar, 1/2 tsp. ground cinnamon
Bake: Bake for ~30-35 minutes Start Timer or until mostly set and the top is golden brown. The middle may sink as it cools, that's just the nature of this recipe...you didn't mess up!
Enjoy: Allow to cool for ~30-45 minutes Start Timer before cutting into wedges (errrr, if you can wait) and then serve with vanilla ice cream. If you slice into the cookie skillet too soon, it might look raw, so that cool time helps the crumb set up. I've found the cookie is chewy and delicious once it has cooled completely, then I'll pop a slice in the microwave and enjoy it smothered with ice cream!
Vanilla ice cream for serving