Puy Lentil Salad with Walnuts and Mustard Vinaigrette

Combine the Dijon mustard, red wine vinegar, sherry vinegar, grated garlic, and maple syrup in a jar. Add the olive oil, seal, and shake vigorously until emulsified. Season generously with salt and pepper.

Finely dice the shallots, slice the celery, pick and chop the parsley, and measure out all remaining ingredients so everything is ready before the lentils finish cooking.

Place the rinsed lentils in a medium saucepan with the cold water, onion halves, whole garlic cloves, bay leaf, and thyme sprigs. Bring to a boil over high heat, skimming any foam, then reduce to a steady simmer and cook for 20–25 minutes until the lentils are just tender with a slight bite — they should hold their shape completely.

Drain the lentils, discard the onion, garlic, bay leaf, and thyme, then immediately transfer the hot lentils to a large mixing bowl. Pour two-thirds of the vinaigrette over them while still steaming and toss well to coat. Leave to absorb for 5 minutes.

Spread the walnut halves in a dry skillet over medium heat and toast for 3–4 minutes, stirring frequently, until fragrant and lightly darkened. Tip onto a board and roughly break them up.

Add the diced shallots, sliced celery, and chopped parsley to the warm lentils and toss to combine.

Fold in the watercress or rocket and the toasted walnuts, then drizzle over the remaining vinaigrette. Taste and adjust seasoning. Scatter the reserved celery leaves over the top and serve immediately.