Step 1

First you’ll need to roast the chiles. Place the chiles under the broiler until blackened, about 5 minutes per side. Place the chiles in a paper sack or plastic food-storage bag, close it tight and let the chiles steam for 20 minutes. Take the chiles out of the bag and gently rub off the skin. Remove the stem and seeds, then slice the chiles from top to bottom to open them up.

Step 2

Preheat the oven to 350°F. Grease a large cast-iron skillet or a 2 ½ quart casserole dish with 1 tablespoon of the butter.

Step 3

To make the salsa, heat the remaining tablespoon of butter in a pan on medium-low heat then add the onions. While stirring occasionally, cook until softened, about 5 minutes. Stir in the garlic and cook for 30 more seconds.

Step 4

Pour into the pan the tomatoes, and add the cumin. While stirring, cook for 10 minutes, then taste and add salt. Turn off the heat.

Step 5

To make the batter, whip the egg whites until so stiff that when you tip the bowl they do not move. Beat the yolks and lightly season with salt, then gently fold the whites into the yolks and gently stir until combined.

Step 6

To assemble the casserole, pour half the salsa into the bottom of the pan. Place on top half the chiles, laying them flat, then evenly cover the chiles with the shredded cheese. Place on top the remaining chiles, laying them flat, then pour over the remaining salsa.

Step 7

Gently spread the batter evenly over the casserole, then bake uncovered until brown and bubbling, 40-45 minutes. Serve warm.