This cake is a mouthful, quite literally. Layers of chocolate and white cake are separated by brownie bits, Oreos, chocolate chip cookies, whipped vanilla buttercream, as well as chocolate buttercream!
Beat butter in bowl of stand mixer with whisk attachment on medium-high speed until light and fluffy. (about 3 minutes)
With the mixer on low, slowly add in confectioners sugar , milk, and salt; frequently scrape sides and bottom of the bowl.
Once incorporated, whip frosting for at least 3 minutes on medium high to high. (My mixer went for 7 minutes)
Remove bowl from mixer and add in Oreo cookie bits. Stir by hand until fully combined. (You can add in more if you want, I just prefer a lighter frosting color so used less Oreo)