For the mashed potatoes, peel and wash the potatoes and cook in salted water for about 20 minutes.
For the horseradish sauce, peel and chop the onion. Heat 2 tablespoons of butter. Sauté onion in it. Add flour and sauté lightly. Stir in 400 ml milk, bring to the boil and simmer for about 2 minutes. Season sauce with horseradish, salt, pepper and lemon juice.
Add the frozen peas and simmer for about 2 minutes.
Boil the eggs for about 8 minutes until soft. Drain the potatoes. Add 200 ml milk and 2 tablespoons butter and mash everything finely. Season to taste with salt and nutmeg. Rinse, peel and halve the eggs. Serve with puree and horseradish sauce.