Step 1
To make the confit garlic, place an oven rack in the centre of oven and preheat to 140°C (120°C fan-forced).
Step 2
Cut tops from garlic bulbs to expose cloves and place in a small ovenproof dish. Pour over enough canola oil to cover garlic (add more oil if needed). Place the dish in the oven and cook for 1 hour or until the garlic is completely soft. Set aside to cool to room temperature.
Step 3
Meanwhile, in a bowl, stir combined mustard, horseradish, Worcestershire sauce and 1 tbs olive oil. Divide into 2 even portions, reserving 1 portion for serving. Season beef. Heat a frying pan over medium-high heat. Add beef and remaining oil. Cook, turning, for 10 mins or until brown all over. Transfer the beef to a roasting pan and brush with remaining portion of mustard mixture.
Step 4
Add the beef to the oven and roast for 1 1/4-1 1/2 hours or until an instant-read thermometer inserted into centre of beef registers 46°C for medium-rare doneness. Set the beef aside for 20 mins to rest.
Step 5
Increase oven temperature to 250°C (230°C fan-forced). Return beef to the oven. Roast for 15 mins or until caramelised and centre registers 54°C. Transfer the beef to a carving board and set aside for 20 mins to rest.
Step 6
While the beef is cooking, to make creamed silverbeet, in a food processor, process bread until coarse breadcrumbs form. In a small bowl, toss breadcrumbs with 1 tbs oil. Trim silverbeet leaves from stems and wash, leaving some water clinging to the leaves. Coarsely chop. Heat a large non-stick frying pan over medium heat and cook silverbeet, in batches, tossing, until wilted. Transfer to a colander to cool.
Step 7
Add remaining 1 tbs oil to the frying pan. Add shallots and garlic and cook, stirring, for 2 mins or until just softened. Place silverbeet in the colander over a bowl and squeeze to remove excess liquid. Reserve 1/4 cup (60ml) liquid. Add the silverbeet to the shallot mixture and toss to combine. Stir in the cream, parmesan and reserved liquid.
Step 8
Transfer silverbeet mixture to a 20cm baking dish and sprinkle with the breadcrumb mixture. Bake at 250°C for 10-15 mins or until the breadcrumbs are golden brown and the mixture is bubbling.
Step 9
Slice the beef and serve with the creamed silverbeet, confit garlic and reserved mustard mixture.