Early last fall, I visited my cousin in Salisbury MA, in the US, and she had bought a whole frozen tenderloin at the DeMoulas Market Basket in Seabrook N.H. She did suspect, however, it not to be the best cut of beef, and it had been pre-marinated as well.
Keen on experimenting we decided to give it the DeMoulas beef the long roast treatment that I had told her so much of. If it ended a disaster, it would hardly matter greatly.
We allowed it to defrost slowly in the refrigerator.
The next day I sealed it by frying it in hot butter, then we placed it in a low oven, i.e. 100C (215F) for a long time (do not remember exactly - but if you leave it for 6-8 hours, that'll most certainly do). If you are daring you could even lower the temperature to 80C (175F) for the same period.
I am happy to say that it ended up as a supreme piece of meat. It remained very moist and exceptionally tender, equally so to a medium beef tenderloin. I suspect that this piece of meat would have been tender any way we would have prepared it.
So there is definitely hope for those preferring beef made well done. This way of baking a tenderloin is certainly more time consuming, but much easier, as you may leave the beef in the oven and remain stress free.
More long roast stories