• Preheat oven to 350°F and line two baking sheets with parchment paper.
• In a large bowl, use a hand mixer with beaters to cream together softened butter and the sugars. Beat until totally combined and smooth, about 2 minutes.
• Add peanut butter and vanilla extract and beat until combined. Add egg and beat until just combined.
• Sprinkle the flour, baking soda, and salt over the mixture and use a spatula to fold everything together until combined and no streaks of flour remain. The dough will be soft and a bit sticky.
• Use a 3 tablespoon cookie to scoop out cookies one at a time (about 15-16 cookies total). Roll each cookie scoop in a small bowl of granulated sugar to coat. Place the rounded scoops onto a cookie sheet about 2" apart and lightly flatten the tops with your fingers.
• Bake cookies one sheet at a time until the cookies are lightly crackled on top and the edges are turning golden, about 10-12 minutes. Don't overbake.
• Cookies will be puffy and then flatten as they cool. Cool on the cookie sheets for about 10 minutes and then transfer to a cooling rack to cool completely.

Chocolate Buttercream

• Mix the butter with a hand mixer and beaters until soft (use a large bowl). Slowly add the powdered sugar, mixing each addition until combined. Add the cocoa powder and mix. This might get a bit messy, so feel free to start adding a bit of the milk to make it a little easier to mix up.
• Add the vanilla extract and add the milk slowly (1 tablespoon at a time) and beat until soft and fluffy, adding additional milk if needed.
• Use a large star tip (like Wilton's 1M) and a piping bag to pipe a large swirl of frosting in the center of each cooled cookie. Alternatively, you can spread a thin layer of frosting on each cookie with a small spatula or butter knife.