Clean, wash and cut the leek into large pieces. Clean, wash and roughly chop the spring onions and watercress. Melt butter in a pot. Stir-fry the leek, spring onion and cress (put some cress aside) briefly while stirring.
Dust with flour and stir in. Gradually add 400 ml water and cream, bring to the boil, cover and simmer for about 10 minutes. Peel carrots, leave some green, wash and cook in boiling salted water for about 10 minutes.
Cut the ham slices in half lengthwise. Drain the carrots, let them drain well and wrap each slice of ham in half. Puree the soup, season with salt and pepper. Arrange in soup bowls, sprinkle with remaining cress and possibly pepper flakes.
Add carrots.