Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a large bowl, cream together the peanut butter, softened butter, granulated sugar, and brown sugar until the mixture is light and fluffy.
Add the egg and vanilla extract to the butter mixture, beating until smooth and fully incorporated.
In a separate bowl, whisk together the flour, baking soda, and salt.
Gradually add the dry ingredients into the wet mixture, stirring until just combined.
Roll the dough into small balls, then roll each ball in a shallow bowl of extra granulated sugar.
Place the balls on the prepared baking sheet and flatten them slightly with a fork in a crisscross pattern.
Bake for 10 minutes, or until the edges are just set.
Remove from the oven and let cool on the pan for 5 minutes before transferring to a wire rack to cool completely.