Creamy razor clam chowder with soy sauce

Ingredients

• 7 razor clams
• 500 ml water
• 1 tbsp unsalted butter
• 1 big onion
• 1 medium size potato
• 1 carrot
• 1/4 celery
• 1 tsp tomato paste
• 2 sprigs thyme
• 1 bay leaf
• 250 ml double cream
• 250 ml fish stock
• 2 tbsp lemon juice
• 4 tbsp Kikkoman Naturally Brewed Soy Sauce
• 14 chives
• 1/2 lemon