There's something so appealing about open-faced sandwiches that most European countries have their own name for them. They're a snack I turn to often because I can take a slice of whatever bread I have on hand and top it with any bits of meat, cheese, relish, or spreads lying about in my fridge. This version is similar to what the Danish call smørrebrød (approximate pronunciation is "smuhr-bruth," but English speakers have a tough time saying the word correctly, so I use the French term for them, tartines). Slices of dense pumpernickel bread and French baguette are topped with a tangy cream cheese mixture and thin slices of smoked salmon and finished with a punchy relish. They're special enough to serve when friends come around, with a creamy Champagne or Chenin Blanc.
Make-ahead: The cream cheese mixture can be made up to 1 day ahead, covered, and refrigerated. The relish can be made up to 4 hours ahead, covered, and refrigerated.1.
To make the relish, in a small bowl, stir the onion, capers, lemon juice, dill, and mustard seeds together. Season to taste with salt. Set aside.2.
To make the sandwiches, in another small bowl, mix the cream cheese, crème fraîche, and chives to blend. Season to taste with salt.3.
Spread the cheese mixture over the toasted slices of pumpernickel and baguette. Cut each slice of pumpernickel bread on the diagonal in half. Top each piece of bread with 1 salmon slice and then with a generous spoonful of the relish.4.
Transfer the tartines to a platter. Using a Microplane grater, finely grate the zest of the lemon over them and serve immediately.