Wipe mushrooms with a damp cloth or paper towel and trim stems. Slice larger mushrooms into 1/4-inch thick pieces; leave small mushrooms whole or halved so pieces are roughly uniform.

Heat pan

Place a large skillet over medium-high heat. Add olive oil and 1 tablespoon of butter; heat until butter is foaming and oil shimmers, about 1 minute.

Sear mushrooms

Add mushrooms in a single layer (work in two batches if necessary to avoid crowding). Let mushrooms cook undisturbed for 3–4 minutes until one side is golden brown, then stir and cook another 2–3 minutes until most pieces are nicely browned.

Aromatics

Push mushrooms to the sides of the pan, add the remaining 1 tablespoon butter. Add the chopped shallot and cook 1–2 minutes until softened. Add minced garlic and thyme and cook 30–45 seconds until fragrant, stirring with mushrooms to combine.

Deglaze

Pour in the white wine or stock to deglaze the pan, scraping up any browned bits from the bottom with a wooden spoon. Cook until the liquid has mostly evaporated, 1–2 minutes.

Season

Stir in kosher salt, black pepper, and lemon juice. Taste and adjust seasoning as needed.

To Finish / Optional

Remove pan from heat. Stir in chopped parsley and, if using, grated Parmesan and red pepper flakes. Transfer mushrooms to a serving dish and garnish with extra parsley.

Serve warm as a side, spoon over toasted bread as a bruschetta topping, toss with pasta, or add to an omelet.