Heat two tablespoons of olive oil in a pan, add onions and sauté for a minute. Add garlic and leeks and continue to sauté till soft. Add potato cubes and hazelnuts and continue to sauté for two to three minutes. Add bay leaf, black peppercorns, salt and three cups of water and cook. Add spring onion greens and cook till the potatoes are completely done. Add basil leaves and mix and cook for a minute.
Remove the bay leaf and strain the soup. Cool the potato mixture and then blend into a smooth puree. Mix the puree with the strained stock and adjust salt. Bring the mixture to a boil.
Add milk, mix and let it come to a boil. Transfer the soup into a serving bowl. Heat the remaining olive oil in another pan, add fresh red chillies and sauté for a minute. Pour the soup into individual soup bowls, garnish with the sautéed red chillies along with the oil and serve hot.