Combine the sour cream, cilantro, lime juice, garlic and salt in a food processor or blender.

Blend until smooth, about 30 seconds, scraping down the sides once.

Add the milk, one tablespoon at a time, blending briefly after each addition, until the crema drizzles off a spoon in a thin ribbon.

Chill at least 15 minutes before serving so it firms up slightly for drizzling.