Preheat the oven to 180°C/350°F.
Smash up the garlic and finely chop the thyme. Brush the whole joint with mustard and a splash of olive oil then cover in the garlic, thyme, salt and pepper.
Crank the heat up to about medium/high. Gently pop the beef into a hot roasting tray or pan sear on all sides until golden brown.
In the same pan whack in the quartered onions, rosemary and garlic, now it's time to get roasting.
Allow to roast for 12-15 minutes per 500g, depending on your desired cooking temperature.
While this is cooking you’ll have time to either get the roasties on, quickly wrap Auntie Fiona’s last minute gift… or start drinking the red wine for the gravy already.
Remove the beef from the oven then transfer the roast to a plate or tray and cover with tin foil and allow it to rest.
Take the roasting pan with all the lovely juices and scraps in it, and place it on a medium heat and carefully whisk the flour into the beef juices.
Cook for 30 seconds then pour in the wine and beef stock.
Allow this delicious gravy to gently simmer a little, and allow the flour to cook out.
Stir in the cranberry and soy sauce then bring to a simmer for around 10 mins, but make sure you are stirring it regularly, (we don’t want everyone bringing up your burnt gravy every Christmas from now on) until the gravy has thickened nicely and is rich and shiny.
Strain all the bits and bobs out of the gravy, the onions, thyme garlic etc.. make sure it’s piping hot.
I would serve this banging roast rump with some creamy mashed potatoes, some thyme roasted sprouts and a sweet and sticky cinnamon spiced red cabbage.