Bread the fish. Spread the flour on a deep plate. Break the eggs into another deep plate (or pie pan) and add ½ teaspoon salt. Beat with a fork until completely liquid. Spread the cornflakes or bread crumbs on a third plate; if you’ve chosen corn flakes (my favorite), use the back of a measuring cup to break them into ¼-inch pieces.
One by one, bread the fish or slabs of squash: dredge a piece on all sides in the flour, coating it lightly and evenly, then use tongs to dip it in the egg, coating all sides, and, finally, move it to the crumbs and press an even coat all around. If time allows, refrigerate the breaded pieces for at least an hour for the coating to set up.
Make the sauce. Roast the tomatillos on a rimmed baking sheet (line it with foil, if you wish, for easy clean up) about 4 inches below a hot broiler. When they have blackened on one side, about 6 minutes, flip them and roast the other side. While the tomatillos are roasting, heat 2 tablespoons of the oil, lard or bacon drippings in a large (4-quart) saucepan over medium-high. When it’s hot, add the onion and cook, stirring regularly, until richly browned, about 7 minutes. Add the garlic and half of the chopped green chile and stir for another couple of minutes. Slide the pan off the heat. Coarsely puree the roasted tomatillos (and all their juice), onions, garlic and chiles in a loosely covered blender. Return the pan to medium-high heat and, when really hot, add the tomatillo puree. Stir for several minutes until the mixture has thickened almost to the consistency of tomato paste. Stir in the broth or water and half of the epazote or cilantro and simmer over medium to medium-low heat for 20 to 30 minutes, for all the flavors to come together.
Make the esquites. In a large (10-inch) skillet set over medium-high, heat the remaining 2 tablespoons of the oil, lard or bacon drippings. When the fat is shimmering-hot, add the corn. Stir regularly until the corn starts to brown, about ___ minutes, then add the remaining green chile. Continue to stir regularly until the corn is richly brown, about ___ minutes longer, then add the remaining epazote or cilantro and stir for a minute more. Remove from the heat.
Fry the fish or squash. You can fry the fish all at once in a large (10-inch) skillet, but the vegetables will have to be done in a couple of batches (or in a very large skillet). A heavy pan will give you the best results. Heat ¼ inch of oil in the skillet over medium. When the oil is hot enough to make an edge of a breaded piece really sizzle, fry them until golden underneath, 2 or 3 minutes, then flip and cook the other side. The fish is cooked when it will flake under firm pressure (it takes a little practice to be able to test the fish without breaking the crust too much. Drain on paper towels.
Finish and serve. Reheat the corn over medium. If the sauce is thicker than a cream soup, add a little water or broth. Taste and season with salt, usually a scant teaspoon, depending on how salty your broth is. Ladle a portion of the sauce into a warm, deep dinner plates. Top with pieces of golden fish or vegetables, then scatter on the warm esquites. Decorate with epazote or cilantro leaves and you’re ready to eat.