Peel, wash and roughly grate the potatoes. Stir in egg. Season with salt and pepper. Heat 2 tablespoons of oil in a pan (approx. 20 cm Ø). Add the potatoes and fry over low heat for about 15 minutes.
Turn the Rösti halfway through the frying time. Clean, clean and halve the mushrooms. Peel onion and garlic and dice finely. Heat 1 tablespoon of oil. Fry the mushrooms in it. Add onion, garlic and prawns and fry.
Stir in the crème fraiche. Season to taste with salt, pepper and lemon juice. Wash the parsley, dab dry, put something aside for garnishing. Cut the rest into fine strips and sprinkle over the ragout.
Serve Rösti with the shrimp ragout.