I am going to make oreo buttercream just by adding crushed up oreos to a normal buttercream mixture but do i just add the biscuit part or the whole oreo including the cream filled centre???

Crush up the whole thing, I say. If you like, you can stick a bunch of cookies in a food processor and grind them up. If you do grind it up really fine, it comes out looking almost like ground coffee. Chunky or fine ... mmmm!

souds lik oreo truffles i make at christmas so i would suggest crushing them add crumbs to your taste for icing i would also make them fine so as not to interfere with design hope this helps

I just crush up the whole cookie and leave some bigger chunks in it, but I have just used it for filling. If I was using it as a buttercream on the outside I'd probably go with smaller pieces.

Just know if you make it ahead of time and let it sit the cookie will absorb some of the moisture in the icing. So I make mine a little softer than I would normally use or you may have to add a little more liquid to soften it up.

What a great idea! I have used Oreos in whipped cream with pudding and that is a definite yum but never in buttercream. Duh. Thanks for the idea.