Preheat the oven according to the puff pastry package instructions, typically around 400°F.

Sauté the onion in a skillet with olive oil over medium heat until translucent, about 3-5 minutes.

Add the finely chopped mushrooms and cook until they release moisture and become tender, about 5-7 minutes.

Season with salt and black pepper, then let it cool slightly.

Combine the cooked mushroom mixture with softened cream cheese and grated Parmesan until smooth.

Roll out the puff pastry on a floured surface and cut into desired shapes.

Spoon a generous dollop of the mushroom filling onto each piece of pastry.

Fold the pastry over the filling and seal the edges well.

Bake in the preheated oven until golden brown and puffed, about 15-20 minutes.