Preheat the oven to 350° F (180° C).
In a small bowl, combine the butter, granulated sugar and brown sugar until completely incorporated.
Stir in the egg yolk and vanilla until combined.
Add the flour, baking soda and salt. Mix until your dough forms.
Fold in the chocolate chips.
Portion the dough out into 6 equal sections and roll into balls.
Arrange on a cookie sheet.
Bake at 350° F (180° C) for 7-9 minutes, until the cookies flatten, spread and no longer look glossy in the center.
Allow the cookies to cool on the pan for 10 minutes prior to transferring to a wire cooling rack.
Store in an airtight container at room temperature for up to 3 days.