How to Make It
Preheat the oven to 350°. Toast the walnuts for about 8 minutes, or until lightly browned. Gently rub off any large pieces of skin and transfer the nuts to a bowl. Add the water and toss to moisten the nuts, then add the brown sugar and a large pinch of salt and toss to coat.
Spread the nuts on a baking sheet lined with parchment paper. Bake for about 10 minutes, stirring a few times, until the walnuts are browned and crisp. Transfer to a plate to cool.
In a small bowl, whisk the vinegar with 1/2 teaspoon each of salt and the pepper. Stir in the olive oil and walnut oil. In a large bowl, combine the endives and watercress. Just before serving, toss the salad with the dressing and scatter the walnuts over the top.