Peel, wash and chop the potatoes. Peel the celery and cut into equally large pieces. Cook potatoes and celery in salted water for about 20 minutes until soft.
Cut toast into small cubes. Peel onion and garlic and dice finely. Knead minced meat, egg, toast, onion, garlic, salt and pepper well. Form about 16 meatballs. Heat 3 tablespoons of oil in a pan, fry the balls for about 10 minutes, turning them over, remove and keep warm.
Clean the mushrooms and chop them if necessary. Clean and wash spring onions and cut them diagonally into rings. Heat 2 tablespoons of oil in a pan. Melt 20 g butter and fry the mushrooms in it. Add spring onions and fry briefly.
Season with salt and pepper.
Heat milk and 30 g butter. Drain potatoes and celery and mash them coarsely. Add milk and mix. Season with salt and nutmeg. Cut cress from the bed. Arrange puree on plates.
Place meatballs and mushrooms on top and sprinkle with cress.