Preheat your oven to 400°F (200°C).

In a skillet, heat 2 tablespoons of olive oil over medium heat. Add 1 cup of sliced mushrooms and sauté for about 5-7 minutes until tender and golden brown.

On a lightly floured surface, roll out your thawed sheet of puff pastry to about ¼ inch thick.

Make slits about 1 inch apart along the long sides of the pastry, leaving the center untouched for your filling.

Spread the sautéed mushrooms evenly along the center of the pastry. Sprinkle 1 cup of shredded Gruyère cheese over the mushrooms.

Fold the slits over the filling, alternating sides to form a braid.

Transfer the braided pastry onto a baking sheet lined with parchment paper. Bake for 25 minutes or until golden brown.