Scrape the salmon skin with a knife to make sure all the scales are removed. Rinse well and pat the fish dry with paper towels.
Heat a large nonstick or cast-iron skillet over medium-high heat (no oil is needed). Place the fillets skin side down in the pan, without crowding. Cover the flesh side of the fish with the salt and cook for about 10 to 12 minutes, until the fish is nearly done. (If the fish is very fresh, I like it best when rare. If you are not so sure about the freshness of the fish, give it an extra minute or two.) Transfer to a plate.
While the fish is cooking, whisk together the egg yolks and one-third of the lemon juice in a small bowl. Whisk in a drop of olive oil; when the oil is completely incorporated, whisk in another drop. Continue adding the oil little by little, whisking continuously, then add more lemon juice until you have a fresh-tasting mayonnaise. (You may not need all the lemon juice.) Whisk in the cayenne pepper and chervil until well blended.
Gently brush the salt from the fish. Place one salmon fillet on each serving plate, and place a dollop of mayonnaise on top of each. Serve the remaining mayonnaise on the side.