Grilled Steak Sandwich with Blue Cheese Coleslaw

Name: Grilled Steak Sandwich with Blue Cheese Coleslaw
Ingredients: For the steak sandwich; 1 flank steak, preferably grass-fed (about 2 1/2 pounds); Salt and pepper; 6 ciabatta rolls; For the blue cheese coleslaw; 5 cups mixed shredded cabbage (green, red, Napa); 4 large carrots, peeled and shredded; 1/2 cup minced sweet onion; 1 tablespoon dijon mustard; 1 tablespoon apple cider vinegar; 2 teaspoons sugar; 1/2 cup mayonnaise; 1/4 cup buttermilk; 1/2 cup crumbled blue cheese; 1/2 teaspoon celery seeds; 1/2 teaspoon celery salt; Salt and pepper, to taste