Today I made a salmon mousse flavored with horseradish, lemon zest and herbs. Whisked egg whites provide structural integrity to the mousse, and cream gives it an airy, ethereal texture. I poached the salmon mousseline in individual molds to keep the salmon moist and tender.
This is a great main course for an elegant Christmas meal. Come back tomorrow to see how I would serve this dish!
Zest and gather 1 teaspoon of lemon zest. Cut 10 thin slices of lemon and juice the rest. Set all 3 aside, separately.
Ask your fishmonger to skin the salmon fillets, get the pin bones removed and keep the bones and trimmings. Pat dry using paper towels. Cube the fillets into small chunks. Season with salt, freshly ground black pepper and cayenne powder. Plastic wrap and chill in the refrigerator for an hour.
Pat the salmon cubes dry one more time. Place the salmon in a food processor. Add the chives, lemon zest, horseradish mustard, pink peppercorns, dill and cream. Briefly pulse the salmon about 3 or 4 times. The salmon should still be chunky. Transfer to a mixing bowl.
In another bowl, whisk the egg whites for about 2 minutes at a low speed. Increase the speed of your mixer and keep beating for another 2-3 minutes until they form soft peaks. Don't over-beat or the texture will become grainy.
Using a silicone spatula, mix 1/3 of the whipped egg whites with the salmon mixture to soften it. Add the rest of the whipped egg whites and gently in fold in the eggs to get an airy batter.
Create 10 (2-1/2-inch) disks and 10 (8-inch by 1-inch) rectangles with parchment paper. Line 10 (2-1/2-inch) round mini-molds with the parchment paper disks. Place the rectangles along the sides of the molds, using the parchment paper as a liner against the wall of the molds. Fill them with the salmon mousse. Top each mold with a thin slice of lemon.
In a pot, make a fish stock. Heat the oil. Add the shallot and cook until translucent. Add the carrot, celery, bay leaf, thyme (see tips). Add 1/2 cup of water if the ingredients start sticking to the bottom of the pot. Cook for about 4-5 minutes. Add the bones and trimmings of the fish and about 6 cups of water. Bring the liquid to a boil. Regularly skim the impurities rising to the surface of the broth using a fine mesh strainer. Add 1 tablespoon of white vinegar, 1-1/2 teaspoons of salt and the whole black peppercorns. Cook for about 30 minutes. Strain the fish stock through a fine-mesh sieve into the soup pot (discard the solids). Place a pop-up steamer basket in the pot. Top with the salmon molds. The level of fish stock should go half-way up the side of the molds. Poach the salmon (see tips) for about 20-25 minutes. Unmold the salmon, remove the lemon slices and drizzle with lemon juice. Garnish with extra dill.
You can serve the salmon mousseline with boiled potatoes and a wasabi-flavored yogurt sauce or a chimichurri sauce (parsley, a lot of olive oil, lemon zest, lemon juice, garlic).
Stay tuned for tomorrow's recipe and see how I dressed the salmon mousseline.
To check the salmon for doneness, gently press the salmon with your finger. If the fish begins to flake, the salmon is cooked. If it isn't done, put the mold back on the steamer basket and poach the salmon for another 5 minutes or until done.
Using a thermometer, the temperature of the fish stock should be between 165°F and 180°F while poaching the salmon.
I poached the salmon in individual molds (the same ones I used for the maple fig tartlets.). The one pictured was poached in non-stick silicone rum baba molds but they were too tall for what how I wanted to dress the salmon mousseline with.
You can find horseradish mustard in most regular chain stores, such as Safeway. Look for the Maille brand mustard.
Do not discard the remaining fish stock; I'll show you how to make good use of it in my next dish. 
For the fish stock, I only used a bay leaf and thyme but the traditional way to make it is with a bouquet garni, composed of sprigs of thyme, 1 bay leaf (torn in half), 1 small portion of leek (only the green part) and a few flat-leaf parsley stems. Gather all the ingredients of the bouquet garni in a large teabag (I buy these at Daiso, the Japanese version of a 99-cent store. They cost $1.50 for 40 tea bags) or a square of cheesecloth and tie it with some twine.

I used a fresh bay leaf from the garden, but you can use the dry version if you can't get your hands on fresh leaves.