Before moving onto the next step, make sure the cookies are cooled.
Scoop the frosting into a piping bag with a large tip.
Frost one side of the cookie sandwich.
Place the second layer on top or the frosted half.
I decided to roll the cookie in various sprinkles to make it a bit more festive, but that’s completely optional.
In the bowl of a stand mixer with the paddle attachment, beat the butter and peanut butter on medium speed until smooth, about 2 minutes.
Gradually mix in the powdered sugar, and continue beating. Add vanilla extract and salt.
As the mixtures starts getting thick, add 1 tbsp of heavy cream at a time until desired consistency. I used about 4 tbsp for a creamy and spreadable frosting. Beat for another 2 minutes until light and fluffy.
Cover and refrigerate until ready to use.
To assemble the cookies, using a spoon or pastry bag, spread the frosting on one side of the cookie. Place another cookie on top and gently press down.