Preheat the oven to 350°F. Line a small baking sheet with parchment paper.

In a small bowl, mix the melted butter, brown sugar, and white sugar until smooth.

Add the egg yolk and vanilla extract, then stir until combined.

Add the flour, baking soda, and salt. Stir gently until a soft dough forms.

Fold in the chocolate chips evenly.

Shape the dough into one thick cookie and place it on the baking sheet.

Bake for 10 to 12 minutes until the edges set and the center stays soft.

Let the cookie cool for 5 minutes before eating.