Preheat your oven to 350°F (175°C) and line a baking tray with parchment paper.

Melt 2 tablespoons of unsalted butter and 2 tablespoons of olive oil in a skillet over medium heat. Add the diced onion and sauté for about 5 minutes until soft and translucent.

Stir in 2 minced garlic cloves and 10 ounces of sliced cremini mushrooms, cooking for about 8 minutes until browned and moisture has evaporated.

Season with 1 teaspoon of fresh thyme leaves, salt, and black pepper to taste. If desired, stir in 1/4 cup of dry white wine and cook until mostly absorbed, then remove from heat.

In the same skillet, stir in 8 ounces of cream cheese and 3/4 cup of finely grated Parmesan cheese until smooth. Fold in 1/2 cup of grated Gruyère cheese until slightly melted.

Let the filling cool for a few minutes, then stir in one beaten egg.

Unroll the thawed puff pastry on a floured surface and make diagonal cuts about 1 inch apart along each side, leaving the center intact.

Spread the mushroom and cheese filling down the center of the pastry. Fold the ends over the filling and braid the diagonal strips over the top.

Transfer the braided puff pastry to the lined baking tray and brush the top with a beaten egg.

Bake for 20-22 minutes until golden brown and flaky.

Allow to cool for about 10 minutes, then sprinkle with chopped parsley before serving warm.