Put a pot of water on to boil. Butter a shallow 2- to 3-quart baking dish.
Heat the broiler on high. Rub the poblanos lightly with olive oil and broil them as close to the element as possible on a baking sheet lined with foil, turning as needed, until the skins are blackened all over. Transfer to a bowl, cover the bowl with plastic, and let cool to room temperature. Turn off the broiler and heat the oven to 350°F. Remove and discard the charred poblano skins, the stems, and the seeds. Chop the chiles roughly and put them in a food processor. In a hot dry skillet over medium-high heat, lightly toast the tortillas until they’re just softened and give off a toasted corn aroma, 30 to 60 seconds per side (don’t let them become crisp). Roughly chop the tortillas and add them to the chiles in the food processor, along with the cilantro leaves. Pulse until finely chopped but not puréed. In a large bowl, whisk together the half-and-half, eggs, salt, and pepper until well combined. Stir in the chopped chile mixture.
A savory custard of eggs and half-and-half, whisked together, binds this mac and cheese.
When the water boils, salt it well and boil the macaroni until al dente, following the package directions. Drain well. Add the pasta to the egg mixture, along with two-thirds of the grated cheeses; stir to combine. Pour the mixture into the buttered baking dish. Scatter the remaining grated cheeses evenly over the macaroni.(If baking in a 2-quart dish, set it on a baking sheet to catch any drippings.) Bake until browned and bubbling, about 40 minutes. If you want to brown the center more, flash it briefly under the broiler. Let it rest ten minutes before serving.