Preheat the oven to 175°C (350°F). Line a baking sheet with parchment paper.

In a small bowl, whisk together flour, baking soda, and salt. Set aside.

In a larger bowl, beat peanut butter, softened butter, brown sugar, granulated sugar, and vanilla extract until creamy. Add the egg yolk and mix well.

Gradually add the dry ingredients to the wet ingredients, stirring until just combined.

Scoop tablespoon-sized portions of dough onto the prepared baking sheet. Flatten each ball slightly with a fork, creating a crisscross pattern.

Bake for 10-12 minutes, or until the edges are golden. Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.