I've made this before, but made a small change to cooking the veg, and it made a huge difference.
For two (plus sandwiches) I used:
900g of rolled beef brisket
1 large sweet potato
3 large carrots
2 beef OXO cubes
Tin (aluminium) foil
1 large frying pan
1 large saucepan
1 roasting dish
1. Put your frying pan on a high heat with oil, fill and turn on the kettle, turn your oven to 150 degrees C. Put the beef on the frying pan, frying all the sides until brown all over; meanwhile, pour boiling water into jug and mix one OXO cube into the boiling water.
2. Once browned, put the beef into the roasting dish, salt and pepper it, pour the OXO stock over it, and cover the roasting dish with a "tent" of foil. Place in the pre-heated oven.
3. After an hour, turn the meat over. Still tented, return to the oven.
4. Repeat 3.
5. After the beef has been in the oven for about two and a quarter hours, peel your carrots and sweet potato (or not) and chop into large chunks (this is not optional).
6. Boil the sweet potato and carrots in salted water for 4 minutes (i.e. parboil them). Drain them with the colander (or as I did, with the lid of the pan, and a scalding). Return them to the saucepan, put the lid on, and shake them about so they get a bit battered.
7. After the beef has been in the oven for about two and a half hours (or once you're done peeling, slicing and parboiling), put the veg in with it, pour oil and salt over the veg.
8. Clean that saucepan.
9. After a total of three hours, take the roasting dish out of the oven, take out the beef and the veg, and pour the juices into the (clean) saucepan. Return the beef and veg to the roasting dish and into the oven at 170 degrees C.
10. Heat the juices over a medium heat. Put a small amount of boiling water into the jug, mix in an OXO cube, and add that to the saucepan. Put a small amount of cold water into the jug, and mix in some (corn)flour with a fork (or a whisk, if you wanna be posh).
11. After a total of three and a half to four hours in the oven for the beef, take the lot out. Slice up the beef, scrape the blackened, but not burnt, veg off the bottom of the pan and pour the gravy over it.
12. Put off washing that roasting dish until tomorrow - honestly, nothing will move that except an overnight soak (or maybe that stuff that black chef advertises on TV).
Volumise: Add some parsnips, turnips or other root veg (not potatoes) to the veg present. Replace sweet potatoes with these to reduce carbs.
Add carbs: Add some more sweet potatoes or some potatoes.
Add fat: Use almond flour in the gravy. Replace some of the water-based stock with olive oil. Pour more oil over the roasting meat and veg at every possible point. Buy a "self-basting" joint, that is one with a block of fat on top.
Add protein: While you're putting the veg into the pan, wrap the beef in bacon (pig for more fat, turkey for less).
Add a hospitalisation: Don't use oven gloves.