At a midsummer midnight feast in Sweden, you're likely to find foods like pickled herring on rye toast with a mustard sauce; potato salad with cornichons, capers, and mustard sauce; or gravlax with, you guessed it, mustard sauce. Swedes like their mustard in winter, too, eating it with foods like potato sausages and yellow pea soups.
The mustard Swedes lean toward is relatively sweet with just a twinge of spicy heat. You could use it like they do in Sweden, made into a sauce with dill and a bit of oil and vinegar. But it's also great spread on a burger, sandwich, or just about anywhere you'd want a dab of mustard.