In a frying pan, sweat the carrots and leeks with butter, but do not brown. Cover with water and leave to simmer. Once vegetables are cooked, blend with a hand blender and put through a sieve.
Put back on the heat and season to taste. Remove from the heat and add the cheese and papaya (reserving a few cubes for garnish). Season generously with nutmeg, stir and refrigerate. Serve chilled, sprinkled with chives and papaya cubes.