Preheat oven to 350℉ or an air fryer to 325℉.
Stir together melted butter and brown sugar in a small bowl until smooth. Add the egg yolk and vanilla extract. Stir until smooth and creamy.
Add the flour, baking soda, and salt. Stir until a dough forms. Add the chocolate chips (and nuts, if using) and mix.
If you have any cookies left, they keep for about three days covered at room temperature.
Don’t have an ⅛ teaspoon measuring spoon? No problem! Fill a ¼ teaspoon spoon half full.