Cover a large griddle with aluminum foil and preheat to medium-high.
2
Cook tomatillos, serrano peppers, and garlic on the hot griddle, turning occasionally, until toasted and blackened — about 5 minutes for garlic, 10 minutes for peppers, and 15 minutes for tomatillos. Remove to a bowl and allow to cool.
3
Heat oil in a small, deep skillet to 350 degrees F (175 degrees C).
