01 -
Preheat oven to 180°C and line a baking sheet with parchment paper.
02 -
Melt unsalted butter with olive oil in a skillet over medium heat. Add diced yellow onion and sauté until soft, about 5 minutes.
03 -
Stir in minced garlic and cremini mushrooms. Sauté until browned and moisture evaporates, about 8 minutes. Season with fresh thyme, salt, and black pepper. Pour in dry white wine if using, and cook until liquid is absorbed.
04 -
Reduce heat and stir in cream cheese, Parmesan, and Dijon mustard until creamy. Fold in Gruyère cheese until melted.
05 -
Unroll the puff pastry on a floured surface, cutting 8 diagonal strips on each side while leaving the center intact for the filling.
06 -
Spread mushroom mixture down the center of the pastry. Fold edges in and braid the strips over the filling, sealing tightly.
07 -
Transfer the braid to the prepared baking sheet. Brush the top with beaten egg. Bake for 20 to 22 minutes until golden brown.
08 -
Allow to cool for 10 minutes before slicing. Garnish with chopped fresh parsley.