Preheat oven & prep pan: Preheat oven to 400°F (200°C). Line a large rimmed baking sheet with parchment paper.

Clean & season mushrooms: Wipe cremini mushroom caps clean with a damp paper towel. Gently snap out and discard stems (or save for broth). Toss mushroom caps lightly in olive oil, salt, and pepper. Arrange hollow-side up on the prepared baking sheet.

Mix Boursin filling: In a medium bowl, combine softened Boursin cheese, softened cream cheese, grated Parmesan, minced garlic, chopped parsley, and red pepper flakes. Beat with a fork or rubber spatula until smooth and thoroughly blended.

Stuff the mushroom caps: Using a small spoon or cookie scoop, generously mound the Boursin cheese mixture into the cavity of each mushroom cap.

Make crunchy topping: In a small bowl, stir together panko breadcrumbs, melted butter, and 2 tablespoons grated Parmesan until evenly moistened. Spoon or sprinkle the buttered panko mixture generously over each stuffed mushroom, pressing gently to adhere.

Bake & broil: Bake at 400°F for 18-20 minutes until the mushrooms are tender and juicy, the cheese is molten and bubbling around the edges, and the panko topping is deeply golden brown and crunchy (broil on HIGH for 60 seconds if extra browning is desired).

Garnish & serve: Let cool for 3-5 minutes so the molten cheese settles slightly. Garnish with fresh minced parsley. Serve warm restaurant-style on a festive platter!