3 serrano chiles, stems removed and coarsely chopped
2 medium garlic cloves, coarsely chopped
1/2 cup coarsely chopped fresh cilantro
1 teaspoon kosher salt
Place tomatillos in a medium saucepan, cover with cold water, and bring to a simmer over medium heat. Cook until tomatillos just give way when pierced with a knife but aren’t falling apart, about 10 minutes. Drain well.
Place tomatillos and remaining ingredients in a blender and blend until almost smooth (do not overblend or the salsa will be thin and watery). You may need to stop the blender and smash down the tomatillos with a rubber spatula to get the blades moving.
Place the salsa in a container with a tightfitting lid and chill in the refrigerator for at least 1 hour before serving. The salsa will keep in the refrigerator for up to 3 days.