Filet de Bouef Grillé avec Mignonnette de Poivre (Grilled Filet of Beef with Pepper Sauce)

Ingredients

• 1 lb. Idaho potatoes, peeled and quartered
• Salt
• 2 tsp. black peppercorns
• 2 fresh rosemary branches, about 8" long
• 2 (6-oz.) beef filets, about 1¼" thick, each cut into 3 pieces
• 5 tbsp. extra-virgin olive oil
• 2 tbsp. fresh chives, finely chopped
• 1 large shallot, peeled and finely chopped
• 3-4 scallions, white parts only, chopped
• 1 large tomato, seeded and finely diced