Preheat the Oven: Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

Prepare the Spinach Filling: In a large skillet, melt the butter over medium heat. Incorporate the diced shallot and sauté for approximately 2-3 minutes until it becomes clear. Then, add the minced garlic and continue cooking for another 30 seconds until it’s aromatic. Pour in the white wine and cook for 1-2 minutes until mostly evaporated.

Cook the Spinach: Add the fresh spinach to the skillet and cook until wilted, about 2-3 minutes. Remove the skillet from heat and stir in the cream cheese until smooth and well combined. Add the breadcrumbs and parmesan cheese, and mix thoroughly. Set aside and let the mixture cool slightly.

Prepare the Puff Pastry: On a lightly floured surface, roll out the sheets of puff pastry. Cut the pastry into four equal rectangles, large enough to wrap around each salmon fillet comfortably. If the sheets are too small, gently roll them out to enlarge.

Assemble the Salmon Wellington: Season each salmon fillet with salt and pepper. Place a spoonful of the spinach and cream cheese mixture in the center of each puff pastry rectangle, spreading it evenly. Place a salmon fillet on top of the filling, then top the salmon with more of the spinach mixture.

Wrap the Salmon: Carefully fold the sides of the puff pastry over the salmon, wrapping it tightly and sealing the edges. Pinch the seams together to ensure the pastry is sealed well, and place each wrapped salmon parcel seam-side down on the prepared baking sheet.

Egg Wash: Brush each pastry-wrapped salmon with the beaten egg to give it a beautiful golden color as it bakes.

Bake: Bake in the preheated oven for 20-25 minutes, or until the pastry is golden brown and crisp. The salmon's internal temperature should be at least 145°F (63°C).

Serve: Allow the Salmon Wellingtons to rest for a few minutes before slicing. Serve with a side of fresh greens, roasted vegetables, or a light salad for a complete and elegant meal.