This is my go to beef roast recipe.  Believe it or not, you don’t have to add any extra liquid.  The onions release more than enough to keep it moist.

2-3 cups onions, thinly sliced
beef pot roast (chuck is good)
salt and pepper
fresh or dried herb like thyme, rosemary, etc. (optional)

Put the onions in the bottom of a crock pot.  Season your cut of meat with salt, pepper, and optional herb.  Place on top of onions.  Cover with lid.  Turn on low until desired tenderness, approx 8+/- hours.  Slice the beef and serve with warm onions and juices.