Wipe mushrooms clean with a damp cloth or gently brush off dirt. Trim tough stems and slice or roughly chop larger mushrooms so pieces are uniform — aim for about 1/2-inch pieces. Smaller mushrooms can be left whole or halved.

Sweat aromatics

Heat a large skillet over medium heat. Add the butter and olive oil. When butter is melted and foaming, add the minced shallot and cook, stirring occasionally, until translucent and fragrant, about 2–3 minutes. Add the garlic and thyme and cook for 30–45 seconds until aromatic, taking care not to brown the garlic.

Sear mushrooms

Increase heat to medium-high. Add the mushrooms in a single layer if possible (work in batches if your pan is crowded). Let mushrooms sear without stirring for 2 minutes to develop color, then stir and cook another 3–4 minutes until well browned and most of their liquid has evaporated.

Deglaze

Pour in the white wine and use a wooden spoon to scrape up any browned bits from the bottom of the pan. Let the wine reduce for 1–2 minutes until mostly evaporated.

Simmer with stock

Add the stock and bring to a gentle simmer. Reduce heat to medium-low and let simmer until the liquid reduces by about one-third, concentrating flavor, about 6–8 minutes.

Finish with cream and seasonings

Stir in the heavy cream, Dijon mustard, and soy sauce. Simmer gently 2–3 minutes until sauce slightly thickens and coats the back of a spoon. Taste and add salt and pepper. Stir in the lemon juice and chopped parsley.

Optional finish

If you want a richer, glossy sauce, remove the pan from the heat and whisk in the cold butter pieces until melted and incorporated.

Adjust and serve

If the sauce is too thick, add a splash of stock to reach desired consistency. Adjust salt and pepper to taste. Serve warm over steak, roasted chicken, pasta, polenta, or roasted vegetables.