Fillet of Beef Sandwiches

Name: Fillet of Beef Sandwiches
Ingredients: 1/4 pound blue d'Auvergne or other creamy blue cheese; 2/3 cup sour cream; 1/3 cup mayonnaise; 1 1/2 teaspoons Worcestershire sauce; 1 teaspoon kosher salt; 1 teaspoon freshly ground black pepper; 1 loaf health or 7-grain bread; 1 1/2 pounds rare fillet of beef thinly sliced, recipe follows; 1 bunch arugula; Kosher salt; Freshly ground black pepper; 2 tablespoons unsalted butter, at room temperature; 1 1/2 pounds whole fillet of beef trimmed and tied; 2 tablespoons melted butter; 1 tablespoon salt; 1 tablespoon coarsely ground black pepper