This classic French combination makes a great autumn and winter salad. Walnuts and apples are always a good mix, and their flavors contrast nicely with the bitter endive. Gruyère cheese has a nutty flavor and adds a bit of protein, as well.
02Quarter the apple and cut away the core, then slice very thin (you should have at least 16 slices). Place in a bowl of water acidulated with 1 tablespoon lemon juice.
03Whisk together the vinegars, lemon juice, mustard, salt, and pepper. Whisk in the oils. Taste and adjust seasonings.
04Drain the apple slices, dry on paper towels, then add to the salad bowl. Toss with the dressing and serve.