Place the unpeeled small onion and garlic, bay leaves, and about 1 teaspoon of the salt in a large saucepan or medium-sized stockpot with 2 quarts of water. Bring to a boil over high heat; reduce the heat to maintain a low rolling boil and cook for 5 minutes.
Add the shrimp and cook another 2 to 3 minutes (depending on their size), skimming off any froth that rises to the top. Quickly lift out the shrimp with a mesh skimmer or slotted spoon, letting them drain well. Place in a bowl and set aside to cool. Remove the onion and garlic from the simmering stock; discard. Add the squid and cook for 3 minutes. Lift out with a skimmer, letting them drain well, and set aside.
Reserve the stock for another purpose (it will make a delicious fish soup).
Peel and de-vein the cooked shrimp; chop fine and place in a large mixing bowl with the squid and crabmeat. Finely chop the peeled medium onion, tomatoes, jalapenos, and fresh herbs, and add to the bowl of seafood. Toss to distribute the ingredients evenly. Sprinkle the cracker crumbs and another 1/2 to 1 teaspoon salt over the mixture and toss very thoroughly. In a medium-sized mixing bowl, beat the egg whites until they form glossy, not-quite-stiff peaks. Add the egg yolks, 1 at a time, beating well after each addition to incorporate thoroughly. With a rubber spatula, gently fold the beaten eggs into the seafood mixture.
In a heavy-bottomed, medium-sized (about 10-inch) omelet pan or well-seasoned skillet with rounded sides, heat the oil over medium-high heat until fragrant but not quite rippling. Reduce the heat to low. Pour or spoon the seafood mixture into the pan, smoothing it firmly with a spatula to spread it evenly without air pockets on the bottom. Cook, uncovered, for 8 minutes. Flip the cake by sliding it back into the pan. If necessary, loosen with a spatula. Cook for another 3 minutes, until golden, on the underside. Transfer to a platter or large plate and serve hot, cut into wedges.
Recipe courtesy of Zarela Martinez