Instructions:
- Heat 1 Tbsp butter in a large skillet over medium-high heat. Add mushrooms and cook without stirring for 3-4 minutes to develop deep colour. Stir and continue cooking until all moisture has evaporated and they are beautifully browned. Remove mushrooms and set aside.
- Reduce heat to medium. Add remaining 2 Tbsp butter. Sauté minced onion until softened (about 3 minutes). Add garlic and thyme; cook for 1 minute until fragrant.
- Sprinkle the flour over the vegetables and butter. Whisk constantly for 1–2 minutes until the mixture forms a pale, nutty-smelling paste (a blonde roux).
- Pour in the sherry or wine (if using). Whisk vigorously, scraping up any brown bits (fond) from the bottom of the pan. Cook until the liquid has almost entirely evaporated.
- Slowly pour in the warm stock while whisking continuously to prevent lumps. Bring the mixture to a gentle simmer.
- Continue simmering, stirring occasionally, for 5–8 minutes until the gravy coats the back of a spoon thickly.
- Stir in the browned mushrooms, Worcestershire sauce, salt, and pepper. Taste and adjust seasonings.
- Garnish with fresh parsley immediately and serve piping hot.