1/2 cup olive oil
6 green serrano chiles
1 3/4-inch-thick slice from medium-size white onion
1/2 garlic clove, peeled
1/2 teaspoon coarse kosher salt

Heat oil in medium saucepan over medium-high heat. Fry chiles until blistered, about 3 minutes. Remove chiles from oil. Cool chiles and chile oil completely.

Line large skillet with foil; heat over medium heat. Add onion and cook until softened and blackened in spots, about 5 minutes per side. Cool.

Cut stems off chiles. Combine chiles, onion, garlic, salt, and 2 tablespoons chile oil in blender; chop finely. With blender running, slowly drizzle in remaining chile oil and blend until thick. (Can be made 1 day ahead; cover and chill.)

Makes about 3/4 cup.