Clean, wash and cut the leek into rings. Put leek into boiling salted water, bring to the boil and blanch for 2-3 minutes. Pour onto a sieve, rinse under cold water and drain well.
Pour the pineapple into a sieve, collect the juice. Cut the pineapple into pieces. Cut cheese into sticks, ham into strips. Mix yoghurt, crème fraîche, lemon juice and about 3 tbsp. pineapple juice. Season to taste with salt and pepper.
Mix leek, cheese, ham and pineapple with the yoghurt sauce and let it stand for about 30 minutes. Season with salt and pepper and arrange on plates. Sprinkle with freshly ground pepper. Serve with a rustic farmhouse or crusty bread.