Sauté mushrooms, onions, and garlic in butter and olive oil until caramelized
Season with thyme, salt, and pepper; let cool
Roll out puff pastry and place filling down the center
Add Gruyère cheese over the mushroom mixture
Cut diagonal strips down each side of the pastry and braid over the filling
Brush with egg wash for shine
Bake at 400°F (200°C) for 20–25 minutes until deep golden and flaky
Garnish with fresh herbs and serve warm
