Preheat oven to 350 degrees. Line a baking sheet with parchment paper or a silipat mat and set aside.
In a small bowl using a handheld mixer, mix together the butter, brown sugar, and granulated sugar until smooth. Add in the egg yolk and vanilla and mix until fully combined.
In a separate bowl, whisk together the flour, baking soda, and salt.
Add the dry ingredients to the wet ingredients and mix until fully combined, then fold in the chocolate chips.
Set dough aside to chill in the freezer for about ten minutes. This will help to keep your cookies from spreading too much.
Remove dough from the freezer and scoop out rounded balls of dough (about two tablespoons each) onto the baking sheet.
Bake for 10-12 minutes. Cookies will be slightly underdone, allow to cool for at least ten minutes on baking sheet, then transfer to a wire rack to finish cooling.