Gravlaxsas (mustard and dill sauce)

1. In a small deep bowl, mix the two mustards, sugar and vinegar to a paste.
2. With a wire whisk, slowly beat in the oil until it forms a thick mayonnaise-like emulsion.
3. Stiri in the chopped dill.
4. The sauce may be kept refrigerated in a tightly covered jar for several days, but will probably need to be shaken vigorously or beaten with a whisk to remix the ingredients before serving it again.