This recipe merges two winter staples – deeply flavorful French onion soup and nourishing lentil soup – into a single, satisfying dish. Developed in the Birmingham test kitchen, this hearty soup combines the sweetness of caramelized onions, the richness of Gruyère, and the earthy depth of French lentils for a meal that is both comforting and substantial.
The Core Principles: Onions, Stock, and Lentils
The success of this soup hinges on three key elements: properly caramelized onions, a high-quality stock, and the right type of lentils. These aren’t just ingredients; they define the character of the dish, ensuring depth of flavor instead of a watery, unsatisfying base.
Mastering Caramelized Onions: Time is Essential
True caramelization isn’t about speed. It requires a slow, patient process: at least 45 minutes, often closer to an hour. The goal is to achieve creamy, deep golden-brown onions with a jammy texture and concentrated sweetness. Rushing this step results in merely browned onions that retain harsh, watery flavors.
- Low and Slow: Maintain medium-low heat and stir frequently, scraping up any browned bits (fond) to prevent scorching.
- Butter’s Role: Starting with butter encourages browning and adds a toasty richness that oil alone cannot provide.
- Deglaze if Needed: A tablespoon of water can prevent burning if the fond develops too quickly.
Sherry, vermouth, white wine, or even red wine or port can be added to enhance the flavor profile after caramelization. Each option contributes unique nuance, but all complement the sweetness of the onions.
Stock Selection: Quality Matters
Traditionally, French onion soup calls for beef stock. However, poor-quality store-bought versions are best avoided. Homemade beef stock is ideal, but excellent results can be achieved with a high-quality store-bought chicken stock. The key is a stock with depth and clarity, as this forms the foundation of the soup’s flavor.
The Importance of French Lentils (Du Puy)
For texture, French lentils du Puy are essential. Unlike red or brown lentils, these retain their shape and bite even when simmered, providing a pleasant contrast to the soft onions and melted cheese. Avoid overcooking; the lentils should be tender yet distinct, not mushy.
The Gratinée: A Cheesy Finale
The final touch is the cheese-capped bread. Use French bread slices cut to fit snugly into the bowls (about ½ inch thick) and toast them until crisp to prevent disintegration. Brush with butter and rub with raw garlic for added aroma. Top each bowl with a generous ½ cup of grated Gruyère before broiling until melted and blistered.
The result is a spoonful that combines stretchy cheese, crisp bread, sweet onions, and earthy lentils – a familiar yet elevated experience perfect for cold weather. The combination offers a balanced meal that feels both indulgent and nourishing.
