Clean, wash and cut the leek into rings. Peel, wash and roughly dice the potatoes. Peel and chop garlic. Heat oil in a pot. Brown leek, potatoes and garlic in it. Pour in broth, add bay leaf and bring to the boil. Cover and simmer for 10-12 minutes
Dice the toast. Mix buttermilk and starch. When the vegetables are soft, pour cream and buttermilk into the soup, bring to the boil and simmer for about 1 minute, stirring continuously. Crumble the cheese and melt in the hot soup while stirring. Remove bay leaf and puree the soup finely with a chopping stick. Season to taste with salt and pepper
Heat the butter in a pan and fry the bread cubes in it until golden brown. Wash the chives, shake dry and cut into small rolls. Arrange the soup in deep bowls and sprinkle with croutons and chives