Wipe the mushrooms with a damp paper towel or soft brush to remove dirt. Trim the stems if needed and slice mushrooms into even 1/4-inch (6 mm) slices; halve small mushrooms so pieces are uniform for even cooking.

Heat pan

Place a large skillet or sauté pan over medium-high heat. Add the olive oil and butter. Heat until butter foams and just begins to brown lightly, about 1–2 minutes; do not let it burn.

Cook aromatics

Add the chopped shallot to the hot fat and cook, stirring, until softened and translucent, about 1–2 minutes. Add the minced garlic and cook for 30–45 seconds until fragrant, stirring constantly to prevent burning.

Sear mushrooms

Add the sliced mushrooms in a single layer if possible. Avoid overcrowding the pan — cook in batches if necessary. Let mushrooms cook undisturbed for 2–3 minutes to develop a golden brown color, then stir or toss and continue to cook until most of their moisture has evaporated and they are nicely browned, about 5–7 more minutes.

Deglaze and finish

If using, pour the white wine into the pan to deglaze, scraping up browned bits from the bottom with a wooden spoon; cook until the wine is mostly evaporated, about 1–2 minutes. Add the stock and continue to cook 1–2 minutes to concentrate flavors. Stir in the thyme, salt, and pepper.

Finish and serve

Remove the pan from the heat. Stir in the chopped parsley and lemon juice if using. Taste and adjust seasoning with more salt or pepper as needed. If serving on bread, toast bread lightly, spoon mushrooms over slices, and sprinkle with grated Parmesan.

To Serve (optional)

Arrange toasted bread or baguette slices on a platter. Spoon warm mushrooms over the toasts, sprinkle with grated Parmesan and an extra pinch of parsley. Serve immediately.