Start with a beef chuck roast. (Most of the time, I throw this in my crockpot frozen.)
Add a packet of dry onion soup mix. If you don't have this, it is fine without it.
On the stovetop, mix up two packets of brown gravy mix according the package. Let it thicken a little bit. Add one can of cream of mushroom soup.
Pour the gravy/soup mixture over the onion mix and roast.
Set the crockpot to high for 5-6 hours or low for 8-10 hours. The meat gets extremely tender.