Spinach Gruyere Puff Pastry

Drain spinach well, pressing between layers of paper towels to remove excess moisture. Melt 2 tablespoons butter in a skillet over medium heat. Add mushrooms and cook, for 5 minutes. Stir together spinach, mushrooms and cheese; set aside. Roll 1 pastry sheet into a 13x11-inch rectangle. Melt remaining 2 tablespoons butter. Brush 1/2 melted butter over pastry. Spread 1/2 spinach mixture over butter. Roll-up, jellyroll fashion, starting with the long side. Repeat procedure with remaining pastry sheet, butter, and spinach mixture. (Wrap rolls in plastic wrap and refrigerate up to two days, if desired.) Cut rolls into 1/4-inch thick slices. Place on lightly greased baking sheets. Bake at 350 ° for 15 to 20 minutes, or until golden brown.