How to Make It
Put the salmon in a glass or ceramic baking dish and spread 3/4 cup of the coarse salt on top. Refrigerate for 4 hours. Turn the fish over, coat with the remaining 3/4 cup of coarse salt and refrigerate for 4 hours longer. Rinse the salt off the salmon and rub both sides with the sugar.
Wipe out the baking dish and line it with a large piece of plastic wrap. Spread half of the onion, cilantro and lemon zest in the dish and set the salmon on top. Cover with the remaining onion, cilantro and zest and wrap the fish snugly in the plastic. Refrigerate the fish in the baking dish and let cure for 12 hours. Pour off any liquid from the dish, turn the salmon package and refrigerate for 12 hours longer.
Unwrap the fish. Scrape off the onion, cilantro and lemon zest and finely chop enough of the onion mixture to yield 1/4 cup; discard the rest. Cut the salmon into 1/2-inch dice and transfer to a medium bowl. Add the chopped onion mixture, the red pepper and jalapeño and toss to combine.
Stir 1/2 cup of the chives, the sour cream and lemon juice into the tartare and season with fine salt and pepper. Sprinkle with the remaining 3 tablespoons of chives and serve the salmon tartare with toast points.