Preheat the oven to 350℉. Line 2 baking sheets with parchment paper.

In a large-size bowl using a handheld electric mixer, beat together the softened butter and eggs until combined. Add the cocoa powder and cake mix to the wet ingredients and mix on low speed until the dry ingredients are well combined - the dough will be very soft. Cover the dough and refrigerate for at least 30 minutes.

When the dough is done chilling, remove from the refrigerator and roll the dough into balls, using about 1 ½ tablespoons of dough per cookie. Place on the prepared pans, 12 cookies per pan, and bake for 10-12 minutes or until the tops start to crack. Let cool on the pan for 5 minutes before transferring to a wire rack to finish cooling completely.

Once the cookies are completely cooled, place the cream cheese, butter, powdered sugar, and vanilla in a medium-sized bowl and beat with a handheld electric mixer on low speed at first increasing the speed to high as the powdered sugar mixes in, beating for 2 minutes until the frosting is light and fluffy.

Sandwich 1 tablespoon of frosting between two cookies and do so with all the cookies and you will have 12 cookie sandwiches in all.