Chill salad plates when you begin preparing your entrée.
When your entrée is almost ready to serve, combine arugula and romaine leaves and separate onto four chilled salad plates. Scatter toasted walnuts evenly among the salads. Pour vinegar into a small bowl and whisk in the EVOO in a slow stream to combine dressing. Season dressing with salt and pepper, then stir in blue cheese crumbles. Ladle dressing evenly over top of salad plates and serve.