Add the butter, brown sugar, and granulated sugar to a mixing bowl and stir with a spoon to combine.
Add the egg yolk and vanilla and stir well.
Mix in the flour, baking soda, and salt to form a dough.
Stir in the chocolate chips.
Shape the dough into a large ball and flatten lightly to form a ball of cookie dough that is about 4 inches in diameter.
Carefully place a piece of parchment paper down in the preheated air fryer basket and place the cookie dough in the center. The dough will spread a bit, so be sure that the parchment is large enough to allow space for spreading.
Air fry for 5 minutes.
Cool for 5 minutes before serving.
Notes
This recipe makes one BIG cookie. You can split the dough in half to make 2 cookies, if preferred. Cook for 4 minutes instead of 5 to keep the centers gooey.