Boil eggs hard in about 10 minutes. Quench and drain
Wash the asparagus. Peel the white, cut off the woody ends. Cut only the ends off the green. Cut the asparagus into pieces.
Peel, wash and coarsely grate the potatoes. Season with salt and pepper. Heat oil in a coated pan in portions. Fry a total of 8 golden brown Rösti from the potato mixture in 2 portions. Keep warm. Bring 1/2 litre salted water to the boil. Cook white asparagus for about 10 minutes, green asparagus for about 5 minutes. Remove and drain, catching the asparagus stock at the same time. Heat the fat in a pot. Sauté the flour in it until golden brown. Deglaze with milk and asparagus stock. Let simmer for about 5 minutes while stirring. Season sauce with salt, pepper and lemon juice. Heat the asparagus in the sauce
Peel and coarsely chop the eggs. Arrange Rösti and asparagus ragout on plates. Sprinkle with chopped egg and garnish with chervil