Ingredients:

  • 4 Tbsp (60g) Unsalted Butter
  • 2 Tbsp (30ml) Neutral Oil (like vegetable or canola)
  • 3 lbs (1.35 kg) Yellow or Spanish Onions, halved and thinly sliced
  • 1 tsp (5g) Kosher Salt, plus more for seasoning
  • 1/2 tsp (2.5g) Freshly Ground Black Pepper
  • 1 Tbsp (15g) Granulated Sugar (optional)
  • 1/4 cup (30g) All-Purpose Flour (or Gluten-Free alternative)
  • 1/2 cup (120ml) Dry Sherry or Dry White Wine (e.g., Pinot Grigio)
  • 8 cups (2 litres) High-Quality Beef Stock (low-sodium preferred)
  • 2 Bay Leaves
  • 1 sprig Fresh Thyme
  • 8 slices (approx. 1-inch / 2.5 cm thick) Baguette, slightly stale preferred
  • 1 clove Garlic, halved (for rubbing)
  • 1 Tbsp (15g) Unsalted Butter, melted
  • 8 oz (225g) Gruyère Cheese, freshly grated

Instructions:

  1. Slice the Onions: Peel and halve the onions, then slice them thinly and uniformly (about 1/8 inch thick). Uniformity is crucial for even cooking.
  2. Sauté and Sweat: Melt butter and oil in a Dutch oven over medium heat. Add the sliced onions, salt, pepper, and sugar (if using). Stir well to coat. Cover the pot and reduce heat to medium-low. Cook for 15 minutes, stirring occasionally, until onions have wilted and released their moisture.
  3. Caramelisation (The Slow Cook): Remove the lid and increase heat slightly to medium. Stir frequently, scraping the bottom of the pot every 5-7 minutes. Continue cooking for 45–60 minutes until the onions gradually turn from pale gold to a deep, rich, mahogany brown. Do not burn them; if brown bits stick, add a tablespoon of water to loosen them up before continuing.
  4. Add Flavour & Thickener (Roux): Stir in the flour and cook for 2 minutes, stirring constantly to cook out the raw flour taste.
  5. Deglaze with Alcohol: Pour in the Sherry or wine. Scrape up all the deeply caramelised fond (brown bits) from the bottom of the pot. Bring to a simmer and cook until the liquid has mostly evaporated (about 3 minutes).
  6. Add Stock and Simmer: Pour in the beef stock, add the bay leaves and thyme sprig. Bring the soup to a boil, then immediately reduce heat to low. Simmer gently, uncovered, for 20 minutes, allowing the flavors to meld. Taste and adjust seasoning. Remove the bay leaves and thyme stem before serving.
  7. Prepare Topping: Preheat the oven grill/broiler. Brush the baguette slices with melted butter. Toast on a baking sheet until light golden brown and crisp (about 3–5 minutes). Rub one side of the toasted bread slices lightly with the halved garlic clove for an extra kick of flavour (optional).
  8. Gratinée Assembly: Ladle the hot soup into oven-safe crocks. Place a toasted baguette slice on top of the soup in each bowl. Pile a generous mound of grated Gruyère evenly over the bread, ensuring it touches the edges of the crock to create a seal.
  9. Broil and Serve: Place the crocks on a sturdy baking sheet and slide them under the preheated grill/broiler. Cook for 3–5 minutes, watching constantly, until the cheese is bubbling, melted, and beautifully golden-brown in spots. Serve immediately, warning diners that the crockery is extremely hot.