Preheat your oven to 350°F (175°C) and line a baking tray with parchment paper.

In a large mixing bowl, cream together softened unsalted butter, creamy peanut butter, granulated sugar, and brown sugar until smooth and fluffy, about 2-3 minutes.

Beat in one egg and a splash of vanilla extract until fully combined, ensuring a creamy mixture.

In a separate bowl, whisk together all-purpose flour, baking soda, and salt. Gradually mix into the wet ingredients until just incorporated.

Scoop portions of the cookie dough, roll into balls, and flatten slightly before placing on the prepared baking tray.

Bake for about 10 minutes, watching for a light golden edge while keeping centers soft.

Cool on the tray for 5 minutes before transferring them to a wire rack to cool completely.

For the filling, beat together softened unsalted butter and creamy peanut butter, then add powdered sugar gradually while mixing. Adjust with milk until smooth.

Spread the peanut butter filling between two cooled cookies to create a delightful sandwich.