Prepare the meat. Place the tenderloin in a vacuum bag, then in a steamer. Cook at 60 degrees for 90 minutes. Next, heat a frying pan with vegetable oil, add a sprig of rosemary, transfer the almost cooked veal to the frying pan and fry the piece on all sides until golden brown.
Make the sauce. Place the onion in a frying pan and fry until golden brown, add the mushrooms, garlic, wine and broth. Reduce the heat to medium and leave the sauce to simmer for 15 minutes. Then add the cream, thyme, salt, pepper and butter. Stir and cook for 4-5 minutes.