Place a large skillet over medium-high heat. Add 1 tablespoon olive oil and 1 tablespoon butter. Heat until butter foams and oil shimmers, about 1 minute.

Sauté mushrooms

Add sliced portabellas in a single layer (work in batches if needed). Let cook undisturbed 3–4 minutes until the undersides are browned. Stir and cook another 2–3 minutes until most liquid has evaporated and the slices are golden.

Add aromatics

Reduce heat to medium. Push mushrooms to the side, add the chopped shallot and minced garlic to the pan and sauté 30–45 seconds until fragrant (do not brown). Stir into the mushrooms. Add thyme, 1 teaspoon salt and 1 teaspoon black pepper and cook 30 seconds more to blend flavors.

Deglaze & sauce

Deglaze with red wine

Increase heat to medium-high. Pour in 1 cup red wine to deglaze the pan, scraping any browned bits from the bottom with a wooden spoon. Let wine simmer and reduce by about half, approximately 4–6 minutes.

Add stock and simmer

Add 1 cup stock and bring to a gentle simmer. Allow mixture to reduce for 4–6 minutes until slightly thickened and flavored.

Finish with cream and seasonings

Lower heat to medium-low. Stir in 1 cup heavy cream, 1 teaspoon Dijon mustard and 1 teaspoon Worcestershire sauce. Simmer gently 3–5 minutes until sauce coats the back of a spoon. If you prefer a thicker sauce, whisk 1 teaspoon flour with 1 tablespoon cold stock to make a slurry and stir in, cooking 1–2 minutes more.

Adjust seasoning

Taste and adjust salt and pepper as needed. If sauce tastes too sharp, simmer 1–2 minutes more; if too thick, add a splash of stock.

Finishing & garnish

Finish and serve

Remove pan from heat. Stir in 2 tablespoons chopped parsley, 1 teaspoon lemon juice (optional) and 2 tablespoons grated Parmesan (optional) until combined. Let rest 1 minute.

Transfer mushrooms and sauce to a warm serving dish. Serve immediately over polenta, mashed potatoes, pasta, or alongside steak. Leftovers refrigerate up to 3 days.