Peel and finely chop the onion. Wash the leek and cut into thin rings. Peel and wash the potatoes and cut them into small cubes
Heat the oil in a pot. Sauté onion cubes and leek for 2-3 minutes. Add potato cubes and deglaze with 450 ml milk and broth. Let the soup simmer for about 20 minutes
Halve the avocados and remove the seeds. Remove the flesh from the skin. Puree the pulp, cream and lemon juice. Stir the puree into the soup, puree again and warm up (do not boil)
Season to taste with salt and pepper. Heat 5 tablespoons of milk and froth up. Arrange soup in bowls and garnish with salmon caviar and milk foam. Serve immediately