• Preheat the oven to 350°F and set an oven rack in the middle position.
• Grease an 9x13-inch baking dish with butter.
• In a large mixing bowl, toss the potatoes with the salt and pepper until evenly coated.
• Arrange some of the potato slices, edges overlapping, in a single layer on the bottom of the prepared baking dish. Sprinkle a quarter of the cheese over the potatoes, and then pour a quarter of the cream over the cheese. Repeat with the remaining potatoes, cheese, and cream, forming 3-4 layers. Pour any leftover cream over top.
• Place in the oven covered with aluminum foil for 40 minets. Uncover and continue baking for addition 20 minets or until the potatoes are tender when pierced with a knife and golden brown on top.
• Let the dish settle on the counter for about ten minutes.
• Sprinkle with fresh thyme, if using, and then serve.

Preheat Oven:

• Preheat the oven to 400 degrees F. (200 degrees C).

Cream Cheese Mixture:

• In a mixing bowl, combine the room temperature cream cheese, thawed and drained spinach, and shredded cheese. Mix until all of the ingredients are well incorporated. Season this mixture with a pinch of salt and pepper to taste. Set the filling aside.

Puff Pastry:

• On a lightly floured surface, roll out the thawed puff pastries sheets into a rectangle.
• Place half of the the cream cheese mixture in the center of each of the puff pastry, leaving some space around the edges.
• Lay the salmon fillets on top of the cream cheese mixture, centered within the puff pastry.
• Season the salmon with salt and pepper to taste.
• Carefully, fold the puff pastry over the salmon and filling to encase it completely. Make sure to seal the edges by pressing them together firmly. Use a little water to help seal, if needed.
• Transfer the Salmon Wellingtons to a baking sheet lined with parchment paper, seam side down.
• Using a sharp knife, make a few slits on top of the pastry to allow steam to escape during baking. This will help prevent the pastry from getting soggy.
• In a small bowl, beat an egg to create an egg wash. Brush the top of the pastry with the egg wash to give it a nice golden color when baked.
• Place the baking sheet in the preheated oven, and bake for approximately 25-30 minutes or until the puff pastry is golden brown and the salmon is cooked to the desired level of doneness. The internal temperature of the salmon should reach 145 degrees Fahrenheit (63 degrees Celsius).
• Remove the Salmon Wellington from the oven, and let it rest for a few minutes before slicing and serving. Service with a lemon wedge.