- In a small bowl, combine the dill, salt, sugar, citrus zests and black pepper.
- In an 11 x 8-inch (28 x 20 cm) rectangular glass dish, arrange the salmon slices in a single layer. Pour the gin or vodka over the salmon. Sprinkle with the salt mixture.
- Cover with plastic wrap. Weigh down with a heavy object such as another glass dish of the same size. Refrigerate for 24 hours. Drain and pat dry.
- On a work surface, dice the salmon into small pieces. Keep refrigerated.
- When ready to serve, in a bowl, beat the cream with a whisk until soft peaks form. Gently fold in the mustard using a spatula.
- Fill the hors-d’oeuvre shells with the mustard cream and top with the gravlax. Garnish each canapé with a dill frond and, if desired, mullet roe.