Instructions:
- Clean and slice all fresh mushrooms to a consistent medium thickness. If using dried porcini, soak them in hot water for 20 minutes, remove, squeeze dry, and roughly chop (reserve the soaking liquid).
- Melt 1 tablespoon of the butter in a large skillet over medium-high heat. Add mushrooms in batches (do not overcrowd) and cook until they have released their liquid, the liquid has evaporated, and they are deeply browned. Remove mushrooms and set aside.
- Reduce heat to medium. Add the remaining 2 tablespoons of butter to the pan. Sauté the onion until softened (about 3 minutes), then add garlic and thyme. Cook until fragrant (about 1 minute).
- Sprinkle the flour over the vegetables and butter mixture. Whisk constantly for 1–2 minutes to cook out the raw flour taste, creating the roux.
- Slowly pour in the dry sherry. Scrape up all the browned bits (the fond) from the bottom of the pan. Let the sherry bubble and reduce by half.
- Gradually whisk in the warm broth and the reserved mushroom soaking liquid (straining it first through a fine sieve). Bring the mixture to a gentle simmer, whisking continuously until the gravy begins to thicken.
- Lower the heat to low. Stir in the reserved browned mushrooms and Worcestershire sauce. Simmer gently for 5–10 minutes to allow the flavours to meld. Taste and adjust seasoning generously with salt and pepper.
- Remove thyme sprigs. Garnish with fresh parsley if desired and serve piping hot.