Preheat the oven to 350℉, then line two large baking sheets with parchment paper and set aside.
Feel free to use a standing mixer, but a large mixing bowl, handheld mixer, or silicon spatula will work fine. Mix the strawberry cake mix and baking powder. Then using the mixer of your choice, add the melted butter, eggs, and strawberry extract. Beat (on low) until fully incorporated and you've eliminated any lumps.
Fold in the freeze-dried strawberries completely. I like a bit in each bite!
Cover and chill the cookie dough in the refrigerator for 30 minutes or in the freezer for 15 minutes. This will help reduce the cookies from spreading.
Once chilled, use a small cookie scoop or a spoon to drop 1 ½ tablespoon-sized balls onto the baking sheets. This will make uniform cookies, best for the cookie sandwiches! Space the balls a few inches apart to leave room for the cookies to spread.
Bake at 350℉ for 8-10 minutes or until the tops of the cookie are set.
As the cookies bake, prepare the buttercream frosting. In a medium mixing bowl, use a handheld mixer to beat the butter and cream cheese until smooth. Add the vanilla extract and salt and mix. Next, add the powdered sugar a little at a time, mixing as you go. Incorporate the powdered sugar until the frosting is mixed completely and lump-free. For a stiffer frosting, consider adding cornstarch one tablespoon at a time until it reaches desired consistency. This will avoid an overly sweet frosting!
When the cookies are set, remove the baking sheets from the oven and allow them to cool for 3-5 minutes. Then, transfer the cookies to a cooling rack to cool completely.
Once the cookies have cooled, use a piping bag to create a spiral layer of icing on the bottom of a cookie. Grab another cookie to place on top and press ever so lightly. Voila! A cookie sandwich! Repeat with the rest of the cookies.