Smørrebrød only sound complicated. You can put whatever you want on them, says chef Nicolaus Balla, who serves the Scandinavian open-face sandwiches at San Francisco's Bar Tartine. Simply slather a creamy spread like butter or sour cream on dense rye bread. Top with classic combos like roast beef and crisp onions, or smoked salmon and scallions—and since they're on view, make sure they look good. Finish with herbs, lemon zest—anything, really, except a second piece of bread.