Rinse and pat dry salmon fillet. If they are too large, cut them into the needed size. Try to have equal sizes so that everything cooks equally well. If there is skin, remove the skin. I also remove grey patches, those are not that good.
4 piece Salmon Fillet
Season your salmon with salt and black pepper on all sides. Keep aside.
1½ Teaspoon Salt, ½ Teaspoon Black Pepper Ground
For the mushroom duxelles:
Slice and cut shallots small.
1 piece Shallot
Rinse mushrooms, pat dry, and cut the mushrooms. Chop them into rough pieces.
4 ounces Button Mushrooms
Rinse and pat dry parsley. Chop parsley fine.
3-4 Tablespoon Parsley Fresh
Heat up your skillet with the olive oil and sauté shallots soft first.
2 Tablespoon Olive Oil
Stir in mushroom and parsley. Season with salt and thyme. Mix it all well and cook over a medium heat setting.
Deglaze by pouring in the white wine. Keep on the same medium to high heat setting. Mix it up.
¼ cup White Wine
Reduce your duxelles, stirring occasionally. Everything should be dry when it's done in the skillet and not soggy. Keep aside.
To assemble:
Preheat oven to 400 Fahrenheit or 200 Celsius.
Cut puff pastry sheets into two.
2 pieces Puff Pastry Sheets
Place a salmon on one puff pastry rectangle. Spread 1 tablespoon mustard per fillet over the fish.
4 piece Salmon Fillet, 4 Tablespoon Dijon Mustard
Spread about 2 tablespoon mushroom duxelles over each fillet and over the mustard layer. Use up everything, there shouldn't be any mushroom duxelles left.
Carefully wrap the puff pastry around the salmon with the layers so that the pastry is well wrapped around and the fish and it is enclosed completely. Cut off any excess pastry dough because excess pastry will turn out raw and uncooked.
Place salmon wellington on a parchment-lined baking tray. Cut a grid design in.
Separate an egg yolk from the whites. Scramble the yolk and brush it over the individual wellington parcels.
1 Egg Yolk
Bake salmon wellington at 400 Fahrenheit or 200 Celsius for about 20-25 minutes or until they appear golden on top. Test and check if the pastry is cooked through on one. The pastry should not be raw or else bake for a little longer (like a few minutes longer).
Serve up still warm as individual wellington.
Video
Notes
1 salmon wellington per person because those are small ones.
Cut larger salmon fillets into two. Each fillet should be about 5 oz or 150 grams. Measure with your eyes. If your fish comes with skin, remove the skin first!
1 pack (US) Mushrooms equals 8 ounces. Use half of it. For the rest of the world, use half as well and adjust as well as possible.
Wine can be substituted with vegetable broth to make it non-alcoholic.