Boil the tomatillos and serranos in salted water to cover until tender, approximately 10 to 15 minutes, and drain it .
Combine coriander, onion, garlic, tomatillos and serranos, blend in a food processor to a smooth texture.
Heat the Lard in a skillet over medium-high heat, when skillet is hot pour the puree and stir for 5 - 6 minutes.
When puree becomes darker and thicker, add Chicken stock and bring it to boil, keep it at simmering temperature for about 20 minutes until it becomes thick enough to coat a spoon, adjust the seasoning with salt and serve.
