Filet de Boeuf au Vin de Marcillac (Filet of Beef with Marcillac Wine Sauce)

Ingredients

• Extra-virgin olive oil
• 2 medium carrots, peeled and chopped
• 2 stalks celery, chopped
• 1 small yellow onion, peeled and chopped
• 3 tbsp. cognac
• 1 cup red wine vinegar
• 3 cups marcillac, cahors, or other hearty red wine
• 3 cups veal stock
• Cracked black pepper
• 4 (6-oz.) beef filets, each about 1½" thick
• Coarse salt
• 2 tbsp. butter, cubed