Preheat oven:Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.
Cream butter and sugars:In a large bowl, beat together butter, peanut butter, granulated sugar, and brown sugar until creamy (about 2 minutes).
Add egg and vanilla:Mix in the egg and vanilla extract until combined.
Combine dry ingredients:In a separate bowl, whisk together flour, baking soda, and salt. Gradually add to the wet mixture, stirring until a soft dough forms.
Shape cookies: Scoop 1-tbsp portions of dough, roll into balls, and place them on the baking sheet about 2 inches apart.
Make the classic fork marks:Flatten each dough ball slightly with a fork, making a crisscross pattern.
Bake:Bake for 9–11 minutes, or until edges are lightly golden. (They’ll firm up as they cool.)
Cool and enjoy: Let cookies cool on the pan for 5 minutes, then transfer to a wire rack.