In a medium mixing bowl, combine the butter, brown sugar and granulated sugar. Mix until light and fluffy.
Add the peanut butter, egg yolk and vanilla to the butter and sugar mixture.
Add the flour, baking soda and salt to the wet ingredients and mix until just combined. Be careful not to over mix.
Cover dough and chill in the refrigerator for 30-60 minutes.
Preheat the oven to 350°. Use your cookie dough scoop or two small spoons and scoop 1.5 tablespoons of dough. Roll the dough between your hands to form nice, round balls. Coat each ball of cookie dough with the turbinado sugar.
Arrange cookie dough balls on a parchment lined half sheet pan. Use a fork to make crisscross marks on the dough.
Bake cookies at 350° for 8-10 minutes or until the edges are just golden brown. The middles will look slightly undercooked. Allow cookies to cool for 15-20 minutes on the sheet pan before moving to a cooling rack.
Notes
Baked cookies can be stored at room temperature, in an airtight container for 2-3 days.