Mexican Onion Soup with Pasilla Chilli

History & Origin

Mexican onion soup is a fascinating adaptation of the classic French onion soup, transformed with the ingredients and techniques of central Mexican cuisine. Its origins trace back to Mexico City restaurants of the mid-20th century, when French cuisine was predominant in high-end establishments, but Mexican chefs began incorporating local elements to create their own identity. The pasilla chilli, whose name means "little raisin" for its wrinkled, dark appearance when dried, adds a complexity of flavours impossible to achieve with European recipes: notes of dried fruit, dark chocolate, earth and a gentle heat that develops slowly on the palate. This dried chilli is one of the pillars of Bajío and central Mexican cuisine. Mexican onion, typically sweeter and milder than European varieties, caramelises slowly over 45-60 minutes until complex sugars develop. This process transforms the onion flavour from sharp and pungent to deeply sweet with caramel notes, forming the aromatic base that distinguishes this soup. In contemporary Mexican cuisine restaurants, this soup is served in individual clay bowls with toasted bread roll and a generous layer of melted Chihuahua cheese. It is a dish that comforts on cold days.