Instructions:
- Melt half the butter in a large, heavy-bottomed skillet over medium heat. Add minced shallots and sauté until translucent, about 3 minutes.
- Add the sliced mushrooms. Increase heat slightly and cook until they have released their moisture and started to brown nicely (approximately 5-7 minutes). Season lightly with salt and pepper.
- If thickening, sprinkle the flour over the mixture and stir continuously for 1 minute to cook out the raw taste.
- Deglaze by adding the Dry Sherry or white wine. Bring to a simmer, scraping up any brown bits (fond) from the bottom of the pan. Reduce by half.
- Remove the pan from the heat source. Pour in the Cognac/Brandy. Return the pan to the heat, tilt slightly, and ignite the alcohol using a long lighter or match. Let the flames burn out naturally. (If skipping flambé, simmer vigorously for 30 seconds).
- Stir in the beef stock, Worcestershire sauce, and Dijon mustard. Bring to a gentle simmer and cook until the sauce has thickened enough to coat the back of a spoon (about 5 minutes).
- Whisk in the remaining cold butter, one tablespoon at a time, until emulsified and glossy. Stir in the heavy cream (if using) and lemon juice. Taste and adjust seasoning.
- Stir in the fresh parsley just before serving immediately over steak or fish.