To make the onion jus cut the red onions in half from top to bottom. Place the onions flat side down and cut 5 thick slices from each half.
Place the butter and oil in a medium saucepan over medium-low heat. Cook the red onions gently with the lid on for 10-15 mins till tender and translucent. Stir often do not allow to burn. Add the bay leaves, thyme and red wine; simmer for 5 mins with the lid off. Add the beef jus and simmer for 30 mins until it has reduced by a good third. To finish take it off the heat and stir in the cold butter, season well and set aside.
As the onion jus is reducing start preparing the salad components. Remove the thin skin from the fuet, cut it lengthways and then roughly chop it up. In a large fry pan over medium heat cook the blue cheese fuet for 2 mins then remove and set aside into a large bowl.
Melt the oil and butter in the fry pan and throw in all the mushrooms. Cook for 10 minutes until they have become tender then add the garlic and broccoli and cook a further 5 mins. Remove and add into the large bowl with the fuet.
Cook your steaks to your liking and allow them to rest for 10 mins. Cut across the grain about 5cm thick and add it to the large bowl. Add ½ cup of onion jus and season well then toss carefully together.
Place along a large platter or onto individual shallow bowls and scatter with hazelnuts and little crumbles of blue cheese. Top with watercress and red radish sprouts. Pour the onion jus into a serving jug and serve alongside slices of fresh ciabatta