1 pound smoked salmon (preferably unsliced), skinned, pin bones removed and fish cut into 1/4-inch dice (about 2 cups)
2 cups 1/4-inch dice seeded seedless cucumber
1/4 cup chopped fresh dill sprigs
1/3 cup chopped red onion (about 1 small), soaked in ice water to cover 5 minutes, drained, and patted dry
2 1/4 cups sour cream
3 tablespoons fresh lemon juice
1 tablespoon freshly grated lemon zest
2 tablespoons cold water
2 1/2 teaspoons (1 envelope) unflavored gelatin
Garnish: thin cucumber ribbons made by cutting 1 large seedless cucumber lengthwise with a vegetable peeler
Accompaniments: assorted toasts and/or crackers
Directions
Lightly oil an 8-by-2 inch round cake pan and line with plastic wrap.
Spread 1 1/4 cups salmon evenly in cake pan. In a bowl stir together remaining salmon, cucumber, dill, onion, sour cream, lemon juice, and zest until combined well.
Put cold water in a small heatproof cup and sprinkle gelatin over it. Set cup in a saucepan and add enough water to pan to reach halfway up side of cup. Heat gelatin mixture over low heat until gelatin is dissolved and stir into salmon mixture. Season mixture with salt and pepper and spoon over salmon in cake pan. Chill mousse, covered with plastic wrap, at least 6 hours and up to 3 days.
To unmold mousse, invert mousse onto plate. Loft off cake pan and peel off plastic wrap.
Garnish mousse with cucumber ribbons and serve with toasts.
