Defrost peas at room temperature. Peel, wash and halve potatoes and cook in boiling salted water for about 20 minutes. Wash the meat, dab dry and season with salt and pepper.
Cover 4 escalopes with a slice of cheese and ham each. Place the remaining schnitzels on top. Whisk the eggs in a deep plate. Turn the stuffed schnitzels one after the other first in 4 tablespoons of flour, then in egg and finally in breadcrumbs.
Heat lard and fry cordon bleu in portions on each side for about 4 minutes. In the meantime, peel and finely dice the onion. Melt the fat. Steam onion for about 6 minutes while turning.
Add peas after 2 minutes. Season with salt, pepper and sugar. Dust with 1 teaspoon of flour. Add stock, bring to the boil and simmer for another 1 minute. Wash parsley, shake dry, pluck leaves from stalks and chop.
Arrange meat, peas and potatoes on plates. Sprinkle with parsley.