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Onion Soup with Sage Brown Butter, Croutons, and Grated Lemon Peel

This elegant caramelised onion soup offers a sophisticated twist on a classic winter warmer. By slowly cooking nearly six kilograms of onions, the soup develops a rich, natural sweetness that is perfectly balanced by a sharp hint of sherry vinegar and bright lemon peel. The addition of sage-infused brown butter provides a nutty depth, while hand-torn croutons add a much-needed crunch to every spoonful.

Ideal as a refined starter for a dinner party or a restorative weekend lunch, this dairy-free dish is surprisingly simple to prepare. The base can be made a day in advance, allowing the savoury flavours to marry and intensify, leaving you with only the quick garnish to finish before serving. This recipe is a wonderful way to elevate humble pantry staples into something truly special.

Continue reading below

Ingredients for Onion Soup with Sage Brown Butter, Croutons, and Grated Lemon Peel

  • 180ml (1 1/2 sticks) butter, divided

  • 5400g thinly sliced onions (about 2.6kg)

  • 1925ml (or more) low-salt chicken broth

  • 350ml 1/2-inch pieces torn crustless country-style bread

  • 16 fresh sage leaves

  • 1 1/2 tablespoons (or more) Sherry wine vinegar

  • 2 teaspoons finely grated lemon peel

How to make Onion Soup with Sage Brown Butter, Croutons, and Grated Lemon Peel

Melt 90ml butter in heavy extra-large pot over medium-high heat. Add onions; sprinkle with salt and pepper and sauté until onions begin to soften, 15 to 18 minutes. Reduce heat to medium and sauté until onions are very tender and deep golden brown, stirring often and adjusting heat as needed, 25 to 30 minutes longer. Transfer 240g caramelized onions to small bowl and reserve for garnish.

Add 1925ml broth to remaining onions in pot and bring to boil. Reduce heat and simmer 25 minutes to blend flavours. Cool slightly. Working in batches, puree soup in blender until smooth. Return to same pot and add more broth by 60ml fuls to thin soup to desired consistency. Season soup to taste with salt and pepper. DO AHEAD: Can be made 1 day ahead. Cover and chill reserved caramelized onions. Cool soup slightly. Chill soup uncovered until cold, then cover and keep chilled. Rewarm caramelized onions and soup separately before continuing.

Melt 2 tablespoons butter in medium nonstick skillet over medium heat. Add torn bread pieces and sauté until bread pieces are crisp and golden, 5 to 6 minutes. Remove from heat and reserve.

Cook remaining 60ml butter in small saucepan over medium heat until golden brown, stirring occasionally, 3 to 4 minutes. Add sage leaves and cook until slightly crisp, 30 seconds to 1 minute. Transfer leaves to small plate; reserve brown butter in saucepan.

Stir 1 1/2 tablespoons vinegar into reserved caramelized onions, adding more vinegar by 1/2 teaspoons fuls, if desired.

Divide warm soup among 8 bowls. Spoon vinegar-seasoned caramelized onions atop soup in each bowl. Sprinkle each serving with croutons and fried sage leaves. Drizzle sage brown butter over each; sprinkle lightly with grated lemon peel and freshly ground black pepper and serve.

Disclaimer

While every effort has been made to ensure the information is accurate and up to date, individual needs may vary and dietary requirements can differ based on personal health conditions. Always check food labels and allergen information before preparing or consuming any recipe. If you have specific health concerns, allergies, intolerances, or are following a medically prescribed diet, seek advice from your GP, pharmacist, or a registered dietitian before making significant changes to your diet or lifestyle.

Article history

The information on this page is peer reviewed by qualified clinicians.

  • 16 Jan 2026 | Originally published

    Authored by:

    UK recipe editors

    Peer reviewed by

    UK recipe editors
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