Preheat your oven to 350°F
Add the butter to your skillet and melt it over medium-high heat on the stovetop. Once it's melted, remove from heat and whisk in the two sugars.
Let the butter and sugars cool down to at most just warm to the touch. For best results, let it come down to room temperature.
While the butter is cooling, whisk the flour, baking soda, salt, cinnamon, and optional pinch of nutmeg in a medium bowl.
After the butter has cooled, add the egg and vanilla and whisk until fully combined.
Add the flour mixture to the skillet and fold it in with a rubber spatula, mixing until the flour is just combined (no more streaks of white).
Fold in the chocolate chips and walnuts if you're using them.
Bake at 350° for 20-25 minutes, or until the edges are golden brown and crisp. Bake more towards the 20 minute side if you like a less-done cookie!
Remove from the oven and let it cool for 10 minutes before serving. Enjoy warm with a big scoop of vanilla ice cream!