Peel, wash and cut the potatoes into pieces. Cover and cook in salted water for about 20 minutes.
Cut the toast into small cubes and fry in 80 g of hot butter until golden brown. Wash the chives, shake dry and chop finely. Cut salmon filet into very thin slices.
Drain the potatoes, press them through a press or mash them finely. Heat milk and stir in 80 g butter and 2⁄3 chives. Season puree with salt and pepper. Spread the mashed potatoes flat on a plate and spread salmon on top.
Sprinkle with croutons and the rest chives. Season with salt, pepper and lemon juice.