Grate or coarsely chop bread and grind finely in the universal chopper. Clean, wash and finely chop the leek. Wash and chop parsley and put something aside for garnishing. Grate cheese. Separate 4 eggs.
Put 125 g breadcrumbs, cheese, leek, parsley, mustard powder, 1 teaspoon salt and pepper with 6 egg yolks and 4-5 tbsp water in a bowl. Knead with your hands to a smooth mixture and let it rest for about 15 minutes.
Clean the salad, wash it and pluck it finely. Wash tomatoes, cut into slices. Peel, wash and chop the cucumber. Mix vinegar, salt, pepper and 1 pinch of sugar. Fold in 3 tablespoons of oil.
Mix lettuce, tomatoes, cucumber and vinaigrette.
Whisk the egg white and put 125 g breadcrumbs in a deep plate. Form approx. 16 croquettes (approx. 5 cm long; approx. 2 cm Ø) from the cheese mixture. Turn the croquettes first in egg white and then in the bread crumbs.
Heat 3-4 tablespoons of oil in a frying pan. Fry the croquettes in it for about 3 minutes until golden brown. Serve with salad and the rest of the parsley. Drink tip: beer, e.g. ale.