Preheat oven to 200c/180c Fan/Gas Mark 6.

Cut string and fat off beef.
In a large pan, brown all sides of the beef.
Put the beef into a large casserole dish, fill dish with boiling water and cover with tinfoil.

Cook in oven for 1 hr and 15 mins.
Take the dish out the oven, uncover, flip beef over (dry side into water).
Top up with more boiling water if necessary, recover and cook again for 1 hour and 15 mins.

Once cooked, take the beef out the oven and uncover corner to let the air out and cool.
Once cool, recover and put into fridge until the beef is solid if you have time (easier to slice).

Remove the beef from the dish and place on plate to cut into desired slice sizes.

GRAVY (optional):
Scoop out any excess white fat from the water left over in the dish.
Put the water into a pot, bring to boil, add more boiling water if there isn't enough and add gravy granules and stir.
(Once the gravy is ready I add the slices of beef into the pot, but that's my preference, you can leave the beef out and put the gravy into a separate jug as I prefer hot beef instead of cold).

Once cooled you can put this into tins and freeze.