Brush the toast with butter on one side and lightly roast on this side on the grill.
Meanwhile, cut the mushroom into 0.5 cm thick slices. Remove the toast from the grill and coat the roasted side with cream horseradish. Then place the mushrooms on the grill and grill for 1 ½ minutes on each side.
Cover the toast with smoked salmon, pepper to taste and drizzle with a squeeze of lemon. Place the mushrooms and the fried egg on top, pepper and then sprinkle with chives.