1Combine crème fraîche, chives, and lemon juice in a nonreactive bowl and mix until thoroughly incorporated. Season well with salt.
2Spread half of the crème fraîche mixture evenly on top of each flatbread, leaving a 1/2-inch border.
3Arrange half of the onion on 1 flatbread, top with half of the salmon, and season with freshly ground black pepper. Repeat with second flatbread. Cut into 2-by-2-inch squares and serve.
Beverage pairing:Champagne Bollinger NV Special Cuvée, France. There’s no better match for smoked salmon than a fine Champagne. A good choice is Bollinger. The salmon’s oiliness is both contrasted and complemented by the prickly, creamy bubbles of the wine. And the smoky flavor of the fish is echoed by the yeasty toastiness of the Champagne, which is partially aged in wood to give it mellowness and smoke.