Start by preheating your oven to 180°C (350°F). Gently wipe the mushrooms clean with a damp cloth, then carefully remove the stems and set them aside.
Finely chop the mushroom stems and set aside. In a skillet over medium heat, melt the butter and sauté the chopped stems with minced garlic and shallots until fragrant and golden, about 3-4 minutes. The kitchen will fill with an earthy aroma.
In a mixing bowl, combine the sautéed stems, breadcrumbs, grated Parmesan, chopped parsley, thyme, a squeeze of lemon juice, and a drizzle of olive oil. Season with salt and pepper, then mix until the filling is moist but crumbly.
Using a spoon or piping bag, carefully fill each mushroom cap with the prepared stuffing, pressing gently to pack it in. Place the filled mushrooms on a baking tray lined with parchment paper.
Bake in the preheated oven for 15-20 minutes, until the tops are golden brown and the mushrooms are plump and juicy. The filling should be bubbling and crispy on top.
For a crispy, golden top, broil the mushrooms for an additional 2-3 minutes, watching closely to prevent burning. Once done, remove from the oven and let rest for 2 minutes.
Serve the stuffed mushrooms warm, garnished with extra herbs or a squeeze of lemon if desired. They should be tender yet hold their shape, with a crispy, cheesy topping that invites you to take a bite.