This is my recipe for a sublimely tender roast:
- Grab a large chuck roast or brisket.
- Start in the evening by smoking or roasting the meat at 225 F until an internal temp of ~150-160 F is reached.
- Place the meat inside of a covered roaster on a metal rack (important) then place in the oven at a rendering temp (say 170 F) overnight and all day until you get home from work. Your oven needs to be calibrated, because holding meat at too low a temp is a safety concern (see the bottom of answer for more).
- Chill over night before slicing and portioning for the most cohesive, moist and unimaginably tender product. You could rest it on the countertop and slice the night of. Just know that the resting time on a large roast is considerable.
You can adjust the time and temperature variables to simplify the recipe further: roast in the oven at 350 F till ~150-160 F internal temp is achieved. Drop oven down to 170 F in a roaster till tender.
The long answer: (Nerd Alert)
Achieving the perfectly tender roast is a complicated subject because the temperatures at which different meat tissues break down are complicated.
Above 140 degrees F you are out of the food safety danger zone. This means you can take your sweet time as long as you are above this mark (this is a broad generalization, see the bottom of answer). At around 160 degrees, collagen and fats begin to break down or 'render', causing meat to become tender and juicy. However, there is a point where the proteins will begin to tense up and toughen (Don't know this off the top of my head, but the hotter you go the tighter they get).
There is a special temperature zone where you can achieve full rendering (maximum tenderness) without encountering dryness. This is achieved by getting the meat out of the danger-zone then holding it within the rendering zone for a very long time, without leaping into the tightening zone.
The reason that a most pot roasts are fall apart tender but dry is because the typical stock pot will eventually simmer on low. Water boils at 212 F at sea level, at which point most meats are fully rendered but dry.
Safety Adendum: Food safety is a matter of temperature and time. The FDA publishes charts that tell you how long a piece of meat has to be held at a given internal temperature to be safe to eat. To say that beef is safe as long as it is over 140 F internal is not strictly correct, as time is also a factor.