Season the topside with sea salt, black pepper and chopped thyme then brush with a little olive oil. Place the beef in a vacuum pouch and seal
Place the pouch into a water bath preheated to 52 degrees and cook for 4 ½ hours. This will give a rare finish
In a saucepan with a little oil gently sauté the sliced onions and garlic until translucent. Turn up the heat to caramelise the onions and when golden in colour deglaze with madeira
Reduce the Madeira until almost gone then add the dried porcini and the beef stock. Reduce further until the sauce is shiny and thickened
Pass the sauce through a fine sieve
To serve, caramelise the beef on all sides, ensuring you crisp up the fat
