roll up each rectangle jelly roll fashion gently pressing the top edge to seal the pastry. Carefully wrap the rolls tightly in plastic wrap or foil. Flatten each roll slightly by pushing gently on the sides so the spirals will be oval-shaped, and refrigerate until the pastry is firm, at least 2 hours. This may be done up to 4 days ahead of time. Preheat oven to 190ºC , and line a cookie sheet (or 2 if you have them) with baking parchment. Remove the rolls from the refrigerator as you are ready to cut them. With a sharp knife, cut the rolls crosswise into 1 cm slices. Place each oval onto the parchment, leaving 4 cm of space between them. Transfer the pan(s) to the middle of the oven, and bake until the tops are lightly browned. With a spatula, turn the spirals over and continue cooking until the second side is lightly browned and the centers are cooked through. If using 2 pans, rotate the pans during baking for even baking. Remove the pans, slide the swirls onto a rack to cool, and continue in the same fashion until all the swirls are baked. Serve warm. NOTE: If using your food processor to chop mushrooms, you will be far more successful if you pulse them several times to reach the desired consistency rather than let the machine run. Over-processed mushrooms are often watery and will not brown.