Defrost the puff pastry according to the package directions. Cut each puff pastry sheet in half and extend each piece carefully. Fill puff pastry middles with spinach. Place the salmon on top of the spinach, fold the pastry covering the salmon, brush the pastry with the egg yolk.

Place the four pieces in a greased oven dish and bake at 350 degrees until the puff pastry is cooked, about 20 minutes. It will be golden and fluffy.

Heat the mushroom soup; do not add water or milk. It should be thick and creamy. To serve, spoon the mushroom soup in each individual plate. This will serve as a sauce. Place the cooked salmon/pastry over the mushroom sauce and garnish.