Sauté asparagus pieces in butter over medium heat with a pinch of salt and pepper until tender, approx. 3 min; set aside.
Combine crème fraîche with chives, lemon juice and a pinch of salt and pepper; reserve.
To Poach Eggs
Bring 1 qt of water and vinegar to a boil in a medium-sized pot. Reduce heat to a gentle simmer. Break an egg into a small bowl and in a single quick, smooth motion, slip the egg out of bowl and into the hot water. Repeat with remaining eggs. Poach 3 1/2 min for soft-cooked yolk. Remove with a slotted spoon, transferring directly onto smørrebrød.
Lightly toast 4 thin slices of bread. Top toast with 2 oz of crème fraîche mixture. Add 1 oz of salmon. Divide asparagus over bread. Add the poached egg. Top with sliced radishes, fresh dill fronds and garnish with lemon wedge. Serve immediately, with a pinch of salt and pepper.