Preparation Mix red onion, sugar, and vinegar in small bowl. Let stand 10 minutes. Meanwhile, mix cream cheese, chives, crème fraîche, dill, and capers in another small bowl. Spread each bread slice with about 1 tablespoon cheese mixture to cover. Divide salmon among 8 bread slices. Sprinkle about 1 tablespoon red onion mixture atop salmon on each bread slice. Top each of 4 salmon-topped bread slices with another salmon-topped bread slice, salmon side up. Top each stack with 1 cheese-covered bread slice, cheese side down, forming a total of 4 three-layer sandwiches. Cut each sandwich into 4 triangles.
Preparation Mix red onion, sugar, and vinegar in small bowl. Let stand 10 minutes. Meanwhile, mix cream cheese, chives, crème fraîche, dill, and capers in another small bowl. Spread each bread slice with about 1 tablespoon cheese mixture to cover. Divide salmon among 8 bread slices. Sprinkle about 1 tablespoon red onion mixture atop salmon on each bread slice. Top each of 4 salmon-topped bread slices with another salmon-topped bread slice, salmon side up. Top each stack with 1 cheese-covered bread slice, cheese side down, forming a total of 4 three-layer sandwiches. Cut each sandwich into 4 triangles.