Peel, wash and quarter the potatoes. Cook in boiling salted water for about 20 minutes. In the meantime, wash the asparagus and cut off the woody ends. Cook the asparagus in boiling salted water at medium heat for about 10 minutes. Wash the fish, dab dry and cut into portion pieces.
Sprinkle with lemon juice and salt. Heat the oil. Fry the fish on each side for about 4 minutes. Wash the thyme and remove the leaves. Melt 2 tablespoons of butter in the frying fat. Season with thyme. Drain potato water. Add heated milk and remaining butter and mash finely. Wash chives and cut into small rolls.
Season with thyme. Drain potato water. Add heated milk and remaining butter and mash finely. Wash chives and cut into small rolls. Arrange asparagus, fish, thyme butter and mashed potatoes on plates, sprinkled with chives. Serve garnished with thyme and lemon