Heat a heavy pot, add some oil and sauté off the bacon, any beef trim, onion, carrots, and thyme, you are looking to caramelize the ingredients, though not BURN!
Once all golden brown, and the aroma hits you in the face, add the red wine and de-glaze the pot.
Allow to simmer down to just below half the liquid volume prior to adding the stock.
Add the bayleaf, bring to a simmer and allow to reduce to half.
Season the beef with salt, then seal off in a hot pan with some oil till sealed on all sides.
Place in a tray in a pre-heated oven at 90c for approximately 1 hour. For medium rare you are looking for an internal temperature of 54c, which you measure through a probe thermometer.
Brown the onions in a hot pan with a little oil till well caramelized, add the pad to the oven and cook till tender.
Once the beef is cooked, remove from the oven and allow to rest for 20 minutes.
Sauté off the mushrooms in oil butter and thyme.
Strain your sauce through a fine sieve,, add to the heat and reduce till you obtain a thicker consistency, approx. half. Then add a little gastric (50%vinegar (WW) & 50% sugar, boiled) and finally whisk in your butter.
Slice the well-rested beef, and arrange on a platter or deep serving dish, scatter the onions on top. Arrange the mushrooms around the center, and either serve the sauce on the side or added to the dish.