Keep the serving plates in the oven at the lowest setting so they are warm when you serve.
Cut the meat into 1 X 5 cm strips, then coat them with flour.
Heat the oil in a frying pan over medium heat. Sauté the finely chopped onion a few minutes until translucent, then take it out of the pan and set aside on a small plate.
Turn the heat up high, add the butter, and brown the pieces of meat in the same pan, until nicely coloured, about 5 min. For large quantities, avoid crowding the meat in the pan and work in batches. Add the warm broth to deglaze the pan. Put the onion back in and season with salt and pepper. Start cooking gently, covered, for about 20-25 min.
Add the thinly sliced mushrooms, then continue to cook an additional 10 min.
In a small bowl, mix the tomato paste with the cream and Worcestershire sauce. Add to the pan and cook over very low heat 3-5 min, taking care not to let it boil. Serve on the warmed plates.