Preheat your oven to 350°F (175°C).

Carefully remove the stems from the mushroom caps and set the caps aside for stuffing.

In a skillet, melt a couple of tablespoons of butter over medium heat. Add the finely minced mushroom stems, chopped onion, and fresh thyme to the pan. Sauté for 5–7 minutes.

While the sautéed mixture cools slightly, take a bowl and combine panko breadcrumbs, grated Parmesan cheese, and freshly chopped parsley.

In another bowl, scoop in the softened Boursin cheese and fold in the cooled sautéed vegetable mixture.

Drizzle a bit of olive oil over the mushroom caps to moisten them, then use a spoon to generously stuff each cap with the creamy Boursin mixture.

Dip the tops of each stuffed mushroom into the reserved panko mixture, coating them thoroughly.

Carefully arrange the stuffed mushroom caps on a baking sheet and bake for about 20 minutes.

For an extra touch of golden perfection, consider broiling the stuffed mushrooms for an additional 1-2 minutes.

Once baked, remove the mushrooms from the oven and let them cool slightly. Serve warm, garnished with additional parsley if desired.