Peel, wash and halve the potatoes. Cook in boiling salted water for about 15 minutes. Boil eggs hard in about 10 minutes, rinse with cold water, peel and halve. Wash, clean and halve the mushrooms. Peel and finely chop the onion.
Drain peppers. Dice cucumbers finely. Heat the fat. Fry onions and mushrooms. Dust with flour. Add cream and stock while stirring constantly and simmer for about 5 minutes at low heat. Stir in mustard. Add paprika, cucumber and capers. Season sauce with salt and pepper.
Add cream and stock while stirring constantly and simmer for about 5 minutes at low heat. Stir in mustard. Add paprika, cucumber and capers. Season sauce with salt and pepper. Warm up potatoes and egg halves in it. Serve garnished with parsley