01 -
Preheat the oven to 350°F. Line a baking sheet with parchment paper.
02 -
Heat unsalted butter and olive oil in a large skillet over medium heat. Add diced onion and cook until soft, about 5 minutes.
03 -
Stir in minced garlic and chopped cremini mushrooms. Sauté until mushrooms are browned and liquid has evaporated, approximately 8 minutes.
04 -
Season the mixture with chopped thyme, salt, and black pepper. Pour in white wine or broth, if using, and cook until liquid is absorbed.
05 -
Reduce heat to low. Stir in cream cheese, grated Parmesan, and Dijon mustard. Mix until smooth and creamy. Add Gruyère cheese and fold until melted.
06 -
Unroll the puff pastry on a lightly floured surface. With a knife, cut 8 diagonal strips along each side, keeping the center intact.
07 -
Spoon the mushroom mixture along the uncut center of the pastry. Fold pastry strips over the filling, alternating sides to create a braid, and seal well.
08 -
Place the braid onto the prepared baking sheet. Brush the top with beaten egg. Bake for 20 to 22 minutes or until golden brown.
09 -
Allow the pastry to cool for 10 minutes before slicing. Sprinkle with chopped fresh parsley before serving.