Seared Salmon with Cider Sauce and Celery Root Purée

Ingredients

• 1 onion, chopped
• 2 tbsp butter
• 6 cups (780 g) peeled and cubed celery root
• 2 cups (500 ml) milk
• 2 cups (500 ml) water
• 1 garlic clove, finely chopped
• 1 small onion, finely chopped
• 1 tbsp butter
• 1/3 cup (80 g) lightly packed brown sugar
• 1 Empire or Cortland apple, peeled, cored and diced
• 1 tbsp (15 ml) cider vinegar
• 1/4 cup (60 ml) ice cider
• 1 1/2 cups (375 ml) beef broth
• 1/4 tsp coarsely ground black pepper
• 1 1/2 lb (675 g) salmon fillet, with the skin, cut into 4 pieces
• 1 tbsp butter
• 2 tbsp chopped flat-leaf parsley