For 8 servings, roll out one sheet puff pastry. Roll with a rolling pin until smooth and flat. Cut into 4 equal portions. Take square and fold over each side about 1/2 inch so that the edges are double thickness. This will better hold the ingredients in the center. Bake in 400 degree oven until golden brown about 20 minutes.
Meanwhile, caramelize onions over low heat in 1 T butter or coconut oil until golden brown about 15 to 28 minutes
Once pastry squares are golden, remove from oven and spoon onions in center of square. Top with blue cheese. Return to oven and bake until cheese melts. Serve immediately.