01 -
Preheat the oven to 350°F (180°C) and line a baking sheet with parchment paper to prevent sticking.
02 -
In a large skillet, melt butter with olive oil over medium heat. Add diced onions and cook for 5 minutes, stirring occasionally, until soft and translucent without browning.
03 -
Add minced garlic and sliced mushrooms to the skillet. Sauté for 8 minutes, stirring frequently until mushrooms are golden and their liquid has evaporated to develop rich flavor.
04 -
Sprinkle thyme, salt, and pepper over the mixture. Pour in white wine if using, allow liquid to boil off while scraping the skillet to lift browned bits, then reduce heat.
05 -
Lower the heat, then stir in cream cheese, Parmesan, and Dijon mustard if desired. Mix until fully melted and combined. Remove from heat and fold in grated Gruyère until smooth and thick.
06 -
Quickly incorporate one beaten egg into the filling to bind it thoroughly, then allow the mixture to cool slightly for easier handling.
07 -
On a floured surface, unroll the thawed puff pastry. Cut eight diagonal strips along each long side, leaving the center intact for the filling.
08 -
Spoon the cooled mushroom cheese filling along the center of the pastry, ensuring it does not overlap onto the strips. Fold the top and bottom ends inward, then alternately fold the strips over the filling to create a braided pattern.
09 -
Transfer the braid using parchment paper onto the prepared baking sheet. Beat the remaining egg and brush evenly over the braid for a glossy finish.
10 -
Bake for 20 to 22 minutes until the braid is golden brown and puffed. Rotate the baking sheet halfway through if browning is uneven.
11 -
Allow the braid to rest for 10 minutes to firm up the filling. Sprinkle chopped fresh parsley over the top before serving warm for best texture and flavor.