Potato and leek soup

Ingredients

• 50 grams butter
• 2 leeks, trimmed, washed and sliced
• 2 celery stalks, chopped roughly
• 3 teaspoons fresh thyme leaves
• 1 garlic clove, minced
• 1.2 kilograms sebago potatoes, peeled and chopped into small pieces
• 1 litre vegetable stock
• 2 cups water
• sea salt
• cracked black pepper
• 3/4 cup cream, plus extra to drizzle
• crusty bread, to serve