1 1/2 cups packed cilantro leaves and tender stems
1/2 cup packed fresh mint leaves
2 green onions, chopped
3 serrano chiles, chopped
2 tablespoons lemon or lime juice
1/2 teaspoon salt
2 garlic cloves, finely chopped (optional)
1/2 cup yogurt (optional)
Whirl all ingredients in a blender until very smooth. Drizzle in just enough water to loosen, about 1/4 cup. Season to taste with more chile, lemon, or salt if you like.
Make ahead: Up to 1 day, chilled.