Roast the Peppers: Preheat the oven to broil and position the rack close to the broiler. Arrange the whole poblano peppers on a foil-lined baking sheet. Broil for 3–4 minutes per side until blackened and blistered.

Steam & Peel: Place the peppers in a sealed zip-lock bag and let them steam for 5–7 minutes. Peel off the skins, remove stems and seeds, and set aside.

Prepare the Batter: Preheat the oven to 350°F and grease an 8-inch baking dish. Separate egg whites and yolks. Beat the whites with a hand mixer until stiff peaks form. On low speed, add yolks one at a time, then incorporate flour, milk, baking powder, salt, and pepper until smooth and fluffy.

Assemble the Casserole: Spread half of the egg mixture evenly in the baking dish. Layer two poblano peppers over the batter, followed by a sprinkle of cheese. Add the remaining roasted peppers and cheese, then finish with the rest of the batter. Top with the last bit of cheese.

Bake: Place the dish in the oven and bake for 30 minutes, or until golden and set. Cool for 5–10 minutes before slicing.

Prepare the Sauce: While the casserole bakes, char the tomatoes, jalapeño, onion, and unpeeled garlic cloves in a cast-iron skillet until softened. Peel the garlic and tomatoes, then blend with onion, jalapeño, tortilla, bouillon, oregano, water, salt, and pepper until smooth. In the same skillet, heat oil, add the blended sauce, and simmer for 3–5 minutes. Adjust seasoning to taste.