1-First, preheat the oven to 350 degrees Fahrenheit and grease the bottom and sides of a 10-inch skillet with the 1-2 tablespoons of softened butter. Set it aside for now to get everything ready.

2-Next, brown the 1 cup of unsalted butter in a pan over medium heat until it turns golden and smells nutty, then let it cool for 10-15 minutes to avoid cooking the other ingredients too fast.

3-Now, in a bowl, add the 1 cup granulated sugar and 3/4 cup dark brown sugar to the cooled butter, and whisk until they’re fully mixed together.

4-Whisk in the 1 large egg, 1 egg yolk, 2 tablespoons whole milk, and 1 tablespoon vanilla extract until the mixture is smooth and creamy.

5-Fold in the 2 and 2/3 cups all-purpose flour, 2 teaspoons cream of tartar, 1 teaspoon kosher salt, and 1 teaspoon baking soda just until combined; the dough will be thick, so don’t overdo it.

6-Press the dough evenly into the prepared skillet, then mix the cinnamon sugar topping with 1 tablespoon sugar and 1/2 teaspoon ground cinnamon, and sprinkle it over the dough for that extra crunch.

7-Bake for 30 to 35 minutes, or until it’s mostly set and golden brown on top. Once done, let it cool for 30 to 45 minutes before slicing and serving, optionally with vanilla ice cream.