Because they use modernist ingredients, these amounts are given in metric by weight. For more information on how to measure modernist ingredients check out this article.
130g white sugar
Combine the white sugar, brown sugar, and salt in a small bowl then mix together well. Sprinkle the coriander and citrus zests over the salmon. Pour half the sugar-salt mixture into a Ziploc bag large enough to hold the fish. Add the fish to the bag and top with the brandy. Cover with the remaining sugar-salt mixture, making sure the fish is entirely covered. Seal the bag and place in the refrigerator with some heavy cans or bottles on it. Flip the Ziploc bag every 12 hours or so to evenly distribute the juices.
The curing process will take 1 to 3 days, depending on how cured you want the salmon. It's easiest to just open the bag and feel the salmon, once it feels like a good firmness it is done.
Once cured, remove the salmon from the bag, rinse off under cold water, then pat dry with paper towels. You can store the rinsed, unsliced salmon in the refrigerator for several days. When ready to serve, thinly slice the salmon.
Prepare an ice bath for the gel to set in.
Place the cream cheese and water in a pot. Sprinkle in the agar and locust bean gum and puree well with an immersion blender. Bring to a simmer while stirring occasionally. Let simmer for 3 to 5 minutes.
Fill a syringe with the gel base, attach it to a section of tubing, and then push the gel into the tubing. Remove the filled tubing and place it into the ice bath. Once the gel has set, 2 to 5 minutes, fill the syringe with air, reattach it to the set tubing, and push the noodle gel out.
Repeat for as many noodles as you want. You can also make several noodles at once if you have multiple sections of tubing.
Once the noodles are made they are ready to be served or they can be covered and refrigerated for several hours.
Combine all the ingredients except the onion and dill in a pot and bring to a boil. Stir until the sugar and salt dissolve completely. Remove from the heat.
Add the onion and dill to the still-hot brine. Let the brine cool then pour it and the onion into the whipping siphon, being sure not to overfill it. Seal the siphon, charge, and shake well. Let the siphon stay pressurized for at least 20 to 30 minutes, either in the refrigerator or on the counter.
Vent the siphon then pour out the pickled onions into a bowl. The pickles are then ready to serve or they can be stored in the refrigerator for several days.
Place some pickled onion on each bagel round. Top with a swirl of cream cheese noodles, a few capers, and some dill then serve.