Prepare Duxelles Filling: In a large mixing bowl, combine softened cream cheese, finely diced red onion, artichoke hearts, shredded Parmesan cheese, fresh thyme leaves, minced garlic, onion salt, and black pepper. Mix until creamy.

Preheat Oven: Preheat your oven to 425°F (220°C). Roll out the thawed puff pastry on a floured surface into two rectangles measuring about 10"x5".

Assemble the Base: Place one salmon fillet at the center of each pastry rectangle. Spoon 4-5 tablespoons of the cream cheese duxelles filling over each salmon fillet.

Wrap the Pastry: Fold the puff pastry over the salmon and filling, pressing the edges together to seal. Use an egg wash to secure the edges.

Cut & Brush: Place the wrapped Salmon Wellington seam side down on a lined baking sheet. Cut slits on top of the pastry and brush with egg wash.

Bake: Bake for 30-35 minutes, or until the pastry is golden brown. Monitor closely during the last few minutes.

Cool & Serve: Allow to cool for 5-10 minutes before slicing and serving.