Clean mushrooms by wiping them with a damp cloth or paper towel to remove dirt. Trim stems if needed. Slice larger mushrooms 1/4-inch thick; leave small mushrooms halved or whole for variety. Aim for uniform pieces so they cook evenly.

Preheat pan

Place a large skillet over medium-high heat and add the butter and olive oil. Heat until butter foams and the fat is shimmering but not smoking (about 1–2 minutes). The oil raises the smoke point of the butter and helps browning.

Sear mushrooms

Add mushrooms in a single layer (do not overcrowd — cook in batches if necessary). Let mushrooms sit undisturbed for 2–3 minutes to develop a golden-brown sear, then stir and cook another 2–3 minutes until most pieces are nicely browned.

Add aromatics

Reduce heat to medium. Push mushrooms to the side and add the chopped shallot; sauté 1 minute until translucent. Stir in minced garlic and thyme and cook 30–45 seconds until fragrant, taking care not to burn the garlic.

Deglaze and finish

Pour in the white wine (or 1/4 cup stock) to deglaze the pan, scraping up browned bits from the bottom. Allow the liquid to reduce by half (about 1–2 minutes). If you prefer no alcohol, use the optional 2 tablespoons stock/water and reduce similarly.

Season and finish

Season with sea salt and freshly ground black pepper. Stir in lemon juice and chopped parsley. Remove from heat and, if using, stir in grated Parmesan until combined. Taste and adjust salt, pepper or lemon as desired.

Serve

Transfer to a serving dish and garnish with additional parsley or a light drizzle of olive oil. Serve warm as a side, on toast, over pasta, polenta or as part of a grain bowl.