In a small bowl, whisk together the walnut oil, 1 tablespoon wine vinegar, shallot, and salt and pepper to taste. Let stand for 30 minutes to allow the shallot flavor to mellow. Taste and adjust the balance as needed.

Preheat oven to 325°F. Toast pecans on a baking sheet until fragrant and nutty, about 15 minutes. Let cool. By hand, break the pecans in half.

Cut each endive in half lengthwise and remove the core. Slice crosswise at 1-inch intervals.

In a large salad bowl, combine the endive, watercress, grapes, and pecans. Add enough of the dressing to coat the greens lightly; you may not need it all. Add the cheese, crumbling it by hand. Toss gently. Taste and adjust the seasoning. Divide among 4 salad plates or serve from the bowl.