Heat the oil and butter in a pan. Add the onion and cook until it starts to caramelize, about 20 minutes.
Add the mushrooms and saute until they start to caramelize, about 20 minutes.
Season with salt and pepper and add the wine, deglaze the pan and cook until it has evaporated.
Roll the puff pastry out to a 12x12 inch rectangle.
Preheat oven to 400 F degrees.
Score a line around the puff pastry 1 inch from the edge.
Spread the blue cheese over the middle of the puff pastry and then spread with the onion and mushroom mixture.
Bake until the a the pastry is golden brown, about 15-25 minutes.