Preheat oven to 350°F. Line a large baking sheet with parchment paper or a silicone baking mat and set aside.
In a medium sized bowl using an electric mixer, beat the peanut butter and butter until smooth. Add in the brown sugar and granulated sugar and mix until fully combined. Add in the egg yolk and vanilla and mix until well combined.
Add the flour, baking soda, and salt and mix until everything is well combined.
Scoop out two tablespoon sized pieces of dough onto the prepared baking sheet (I usually get about 7 cookies). Gently press down with a fork on the top of each cookie to make a small criss-cross pattern.
Bake at 350°F for 9-10 minutes.
Remove cookies from the oven and let them cool on the baking sheet for 10 minutes. Transfer to a wire rack to finish cooling.
Notes
Prep time includes cooling time for the cookies. Store cookies in an airtight container at room temperature for up to five days.