Prep: Clean and slice mushrooms evenly (~¼" thick). Mince shallot and garlic. Measure wine, stock, and have butter cubed if using.
Heat pan: Place a heavy skillet over medium-high heat until hot. Add 1 tbsp butter + 1 tbsp olive oil (or 2 tbsp oil).
Sear mushrooms: Add mushrooms in a single layer (work in batches if needed). Let sit undisturbed 2–3 minutes to brown, then stir and brown another 2 minutes. Season with ¼ tsp salt while searing. Remove browned mushrooms to a bowl.
Sauté aromatics: Reduce heat to medium. Add 1 tsp butter or a splash of oil if the pan is dry. Sauté shallot 1–2 minutes until translucent. Add garlic and cook 20–30 seconds until fragrant. Add tomato paste now (if using) and cook 30–60 seconds.
Deglaze with wine: Pour in ¾–1 cup dry red wine. Scrape the pan to release browned bits (fond). Bring to a simmer and reduce by ~half (3–6 minutes) to concentrate flavor and cook off some alcohol.
Add stock & mushrooms: Stir in 1 cup stock, thyme, Worcestershire (if using), and return mushrooms (and any juices) to the pan. Simmer gently until sauce thickens and coats the back of a spoon, about 8–12 minutes. Taste and adjust seasoning.
Finish: Remove from heat. For a glossy monté, whisk in cold cubed butter 1 piece at a time until emulsified. For a creamier sauce, stir in 2–4 tbsp heavy cream and warm through (do not boil). Brighten with 1–2 tsp balsamic vinegar or a squeeze of lemon, if desired.
Serve: Spoon over steak, pork chops, roasted chicken, pasta, gnocchi, polenta, or mashed potatoes. Garnish with chopped parsley.