Preheat oven to 350° F. Line a baking sheet with parchment paper.
Beat cake mixes, oil and eggs together in a mixing bowl on medium speed until well combined. Spoon dough balls onto the baking sheet. This is easiest done with a cookie scoop, I like to use the 1.5 Tablespoon size for these. Bake for 7-10 minutes. Most cookies are done when the tops are matte and the edges are set, but these need to bake a little longer or they are gooey. I like to bake them until they are puffy and an inserted toothpick comes out mostly clean.
While the cookies cool, make the filling. Beat softened cream cheese and butter together on medium speed until perfectly smooth. Add vanilla and beat to combine. Add the powdered sugar and mix on low until well combined and no lumps remain. Spread the filling generously on the bottom of cookie, then top with another cookie. Enjoy!
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Notes
You can use any chocolate cake mix for these, but the Devil's Food tastes the most like OREOs.
You don't want the cream cheese and butter at room temperature (unless you're room temperature is in the upper 60s). I recommend getting the butter out about 30 minutes before use and the cream cheese about 40 minutes. For the butter, you want to be able to make an indent on it when you push on it with your finger, but you don't want it to be soft or mushy.
If your powdered sugar is super lumpy, you may find it helpful to sift the powdered sugar before adding it.
Don't want so many cookies? Make a half batch without any problems. The measurement for the oil is 6 Tablespoons.
When adding the filling, I like to make sure my cookies are the same size. They don't work as well when the cookies are different sizes.
If your filling is too loose, simply place it in the refrigerator for about 20 minutes before using.