Combine the red and white wine vinegars, shallots, salt and pepper in a small bowl. Add the oil, stirring well with a whisk.
PREPARE THE SALAD:
Put the apples in a medium bowl. Pour the dressing over them, toss, cover and refrigerate.
When ready to serve, put the endive leaves in your salad bowl, Spoon the apples and the dressing over the endive leaves. Toss to coat. Divide the endive and apples among six plates. Top with blue cheese crumbles and chopped walnuts.