Preheat oven to 350 degrees Fahrenheit. Line 2 baking sheets with parchment paper and set them aside.

In the bowl of your stand mixer, cream the butter, white sugar and brown sugar on high speed until the mixture is light and fluffy. Add the eggs and the vanilla and mix on medium speed until they're fully incorporated, scraping down the sides of the bowl as needed.

Add 1/2 cup of peanut butter chocolate spread into the butter mixture.

Beat the mixture on medium speed until everything is combined.

In a separate bowl, combine flour, cocoa powder, baking soda and sea salt and whisk them together with a whisk or a fork.

Add dry ingredients to the butter mixture and mix on low speed, just until everything is combined, scraping down the sides and bottom of the bowl to incorporate all the ingredients evenly.

Scoop out small mounds of dough onto the baking sheets you prepared. It's best to use a small (1 tbsp) ice cream scoop for this job to ensure each cookie is uniform in size and shape.

NOTE: You'll measure out 48 balls of dough total. However, it's a good idea to measure out only enough dough to fill one or two baking sheets at a time, bake them, and then measure out enough for another 1 or 2 batches.

Bake each sheet for 8-10 minutes at 350 degrees Fahrenheit or until the tops of the cookies just lose their shine. Remove the baking sheets from the oven and let the cookies cool on the baking sheet for a few minutes before transferring them to a cooling rack to cool completely.

While the cookies are cooling, refrigerate the jar of Reese spread in the fridge for 10-15 minutes.

Once the cookies have cooled completely and the Reese spread has been refrigerated, add the Reese spread to a piping bag fitted with a medium star tip.

Pipe one swirl of the spread onto the bottom side of a cookie and then lightly press the bottom of another cookie on top just until the two are stuck together nicely.

Continue this process until you've sandwiched all the cookies (you should end up with 24 cookie sandwiches).