Add the fat to a large stainless steel, carbon steel, or cast-iron frying pan over high heat and heat until it begins to smoke lightly.
Place in the mushrooms, season with salt, and cook for 2 minutes without touching them.
Sauté the mushrooms for 6-8 minutes or until they are well browned.
Scoot the mushrooms to 1 side of the pan, and in the other, the shallots, garlic, and 1 tablespoon of butter.
Cook the shallots and garlic on that side of the pan for 1 to 2 minutes or until lightly browned.
Mix all the ingredients in the pan together.
Remove the pan from the heat and deglaze with the brandy.
Return the pan to the cooktop and cook for 30 to 45 seconds or until all the alcohol has been absorbed into the mushrooms.
Set the mushrooms to the side.
Pour the beef stock into the pan and cook on high heat until it is reduced by one-half.
Add the heavy cream and continue cooking until there is about 1 to 1 ½ cups of sauce.
Put the cooked mushrooms back in and finish by stirring the remaining 1 tablespoon of butter, thyme, parsley, salt, and pepper.
Serve in a bowl or in the pan.
Notes
Make-Ahead: For freshness, you can make this recipe up to 2 days ahead. Keep cool until ready to use.How to Store: Cover and keep in the refrigerator for up to 4 days. You can freeze this covered for up to 3 months. Thaw it in the refrigerator before reheating.How to Reheat: Add the desired amount of mushroom sauce to a small saucepot and heat over low heat until hot. If you’d like this to be saucier, add 3 tablespoons of roux to the beef stock as soon as it’s boiling in the pan. This will immediately thicken the sauce to the desired consistency. You can also add in the cream once it’s thickened.Other mushrooms you can use are chantarelles, maitakes, trumpets, or porcinis.Mushrooms are similar to spinach; once they start to cook, they will lose moisture and shrink considerably in size.