Making the Sauce
Step1
Poach fish fillets in salted water to cover until just done. The fish should barely be flaky.
Step2
Remove fish or seafood to a cutting board and save the poaching liquid for the sauce. Using two forks, shred into small strips.
Step3
Drain the tomatillos. Puree the roughly chopped portion of the onion, tomatillos, jalapeño, garlic and cilantro in a food processor.
Step4
Heat 1 tbsp. lard or oil in a saucepan over medium-high heat. When the oil is hot, add a drop or two of the puree.
Step5
If the puree sizzles when it hits the oil, you're ready to add the rest of the puree. Let the puree cook for 3 to 4 minutes, stirring occasionally, until it takes on a slightly darker color.
Step6
Add 1 3/4 cup of the seafood poaching water and the clam juice. Simmer until the sauce takes on the consistency of gravy (about 8 minutes).
Step7
Taste for seasoning and add salt if necessary. Keep sauce warm while assembling the enchiladas.
Assembling the Enchiladas
Step1
Preheat the oven to 350 degrees F.
Step2
In a bowl, combine the shredded fish or seafood, mayonnaise, salt, minced onion and half the tarragon.
Step3
Heat the remaining lard or oil in a small sauté pan. Using tongs, dip a tortilla in the pan for a second or two, just enough to soften it.
Step4
Take a large plate and put several tablespoons of the tomatillo sauce on it. Put the tortilla on top of the sauce and then flip it over.
Step5
Place 2 or 3 tablespoons of the fish or seafood mixture in a line across the middle of the tortilla. Using your fingers, bring the two edges opposite the mixture over each other to form a snug roll around it.
Step6
Put the tortilla flap side down in a glass baking dish. The dish should hold all rolls snugly in a single layer.
Step7
Repeat the process with the remaining fish or seafood mixture and tortillas. Pour the remaining sauce over the rolls.
Step8
Cover the dish with tinfoil and place in the oven for 8 to 9 minutes. Remove the dish from the oven and garnish with the cheese and a light sprinkle of the remaining tarragon.