In a small nonstick skillet, melt the butter over medium-low heat.
Add the diced tomatillos and sauté for about 1 minute, just until they begin to soften and become fragrant.
Stir in the cooked, diced chicken and continue to cook for another minute to heat through.
Reduce the heat to low.
Add the mayonnaise, heavy cream, grated cheese, scallions, and cilantro to the pan.
Season with salt and pepper.
Stir continuously until the cheese is completely melted and the sauce is smooth and creamy. Be careful not to let it boil.
Immediately pour the mixture onto a serving plate, using a spatula to scrape every last drop of the delicious sauce from the pan.
Before dicing your tomatillo, be sure to remove the papery husk and rinse the sticky film off the fruit under cool water.
Keep the heat on low once you add the cream and cheese. This prevents the sauce from separating or breaking, ensuring a smooth, velvety texture.
