Ingredients :

• Veal tenderloin — The most tender cut of the animal, located along the spine. Ask your butcher for a tenderloin of about 600 to 700 g for 4. Check that it is 4 to 5 cm thick—too thin, and it cooks too fast and becomes dry before you notice.
• Button mushrooms — Choose them firm, with tightly closed caps. As soon as the gills are visible under the cap, they have passed their peak and will release too much water. No need to look for sophisticated varieties here—ordinary button mushrooms have exactly the right texture for this sauce.
• Heavy cream — Full-fat, not light. The fat content is what gives the sauce its coating texture and flavor. With light cream, you’ll end up with something watery and quite bland—all the hard work in the pan will go to waste.
• Dijon mustard — Marked as optional in many recipes, but frankly essential in practice. One tablespoon in the sauce and it immediately finds its balance. Without it, the cream remains sweet to the point of being a bit flat.