1. Preheat your oven to 350°F and line a baking sheet with parchment paper.

2. Cream together the softened unsalted butter, creamy peanut butter, granulated sugar, and brown sugar until light and fluffy. Beat in the egg and vanilla extract until well combined.

3. In a separate bowl, whisk together the all-purpose flour, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, stirring just until a soft dough forms.

4. Use a cookie scoop to portion the dough into 1-inch balls. Gently roll each ball between your palms to smooth it out, then use your fingers to elongate it into an oval shape. Place the shaped cookies on the prepared baking sheet, spacing them about 2 inches apart. Using a fork, lightly press a crisscross pattern onto the top of each cookie, then sprinkle them lightly with extra granulated sugar.

5. Bake the cookies for 8 to 10 minutes, or until the edges are just lightly golden. Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.

6. While the cookies are cooling, make the peanut butter filling. In a medium bowl, beat together the creamy peanut butter and softened unsalted butter until smooth. Gradually add the powdered sugar and vanilla extract, mixing until the filling is light and creamy. If the consistency is too thick, add a tablespoon of milk at a time until it reaches your desired spreadability.

7. Once the cookies are completely cooled, spread or pipe the peanut butter filling onto the flat side of one cookie. Top it with another cookie to create a sandwich. Repeat this process with the remaining cookies and filling.