First, make the filling. Combine all ingredients in a stand mixer fitted with the paddle attachment and beat at medium-low speed until light and fluffy. Transfer to a resealable container and refrigerate until just before you’re ready to use.
Next, make the cookie dough. In a medium bowl, sift together the flour, cocoa powder and baking soda.
Place the butter in a stand mixer fitted with the paddle attachment and beat on medium-low until smooth. Add the salt, beat for an additional 15-30 seconds, then add the sugar and beat until fluffy, about 2 minutes.
Add the flour mixture to the butter mixture in two additions, mixing until a crumbly dough comes together.
Dump dough out onto a piece of plastic wrap and mold into a 6-inch square block. Wrap block up in plastic wrap and refrigerate for 1 hour or up to 2 days.
After dough has had time to set up in the refrigerator, remove both the dough and frosting so they have a little time to soften up. You’ll want the dough soft enough to roll out with a rolling pin and the frosting soft enough to scoop into a piping bag and pipe onto the cookies.
Preheat the oven to 325 degrees Fahrenheit and line two cookie sheets with parchment paper.
Place the dough between two sheets of parchment paper and, using a rolling pin, roll it out to approximately 1/8-inch thick, rotating the dough as you roll it to avoid cracking.
Once dough is rolled out, use a 2 ½-inch round cookie cutter to cut it into cookies. Place on prepared cookie sheets and bake for 9-11 minutes, rotating the pans halfway through.
Remove cookies from oven and let cool completely before adding the filling. When cookies are cool, scoop the frosting into a piping bag and pipe a ring of frosting about ¼-inch in from the edge on every other cookie (the frosting will smoosh out to the edges once you top the frosted cookies with the plain cookies.)
Enjoy your “Boo-zy” Oreos right away or refrigerate them until ready to eat, up to a few days.