Soupe à l'Oignon Gratinée with Braised Lentil and Kale Medley

Melt butter with olive oil in a large heavy-bottomed pot over medium-low heat at 110°C; add thinly sliced onions with a pinch of salt and cook for 40–50 minutes, stirring occasionally, until deeply golden and jammy.

In a medium pot, heat olive oil over medium heat at 160°C; sauté finely chopped onion and minced garlic for 3–4 minutes until softened and fragrant; add rinsed lentils and vegetable broth, bring to a simmer, cover, and cook for 35–40 minutes until tender but not mushy.

Add minced garlic to the caramelized onions and cook for 1 minute over medium heat at 160°C until fragrant; pour in white wine and scrape up all caramelized bits from the pot bottom; let it reduce by half over 3–5 minutes, then add broth, thyme, and bay leaf; simmer at 90°C for 20 minutes and adjust seasoning.

Stir chopped kale into the lentils during the last 10 minutes of cooking at 90°C, allowing it to wilt and soften; finish with a squeeze of lemon juice for brightness just before serving.

Preheat grill to high at 250°C; ladle soup into oven-safe bowls, top each with a generous layer of grated Gruyère, and place under the grill for 3–4 minutes until the cheese is deeply bronzed and bubbling.

Spoon the lentil and kale medley into small bowls or plates while the soup is under the grill, ensuring it’s ready to serve simultaneously at the end of grilling.