The original recipe shows it being served on cucumber slices, but I like it better on Garden Herb Triscuit crackers. This is a favorite with our guests. I find the smoked trout in the refrigerated fish shelves in my supermarket.
Smoked Trout Mousse on Cucumber Slices
from Martha Stewart's Hors D'oeuvres Handbook

1 4-ounce piece smoked trout
2 tbsp heavy cream
Kosher salt and freshly ground black pepper
1 tbsp fresh lemon juice
1 tbsp fresh or prepared grated horseradish
8 oz. cream cheese, at room temp.
1 seedless cucumber, cut into 1/4" slices (I like them thinner)

Remove skin and bones from trout. Put the flesh into the bowl of a food processor and chop until very fine. With the machine still running, add the cream in a steady stream. Add the salt and pepper, lemon juice, and horseradish.

Transfer the mixture to a bowl and add the cream cheese. Blend until well combined and smooth. Using a rubber spatula, press the mixture through a fine sieve to remove any lumps. (I skipped this part) Refrigerate until ready to use.

Using a pastry bag fitted with a star tip pipe a rosette of mix onto the center of each cucumber slice.

Note: I use disposable pastry bags because I don't see how you could get the fish smell out of a reuseable bag! Also, fresh out of the fridge you will not be able to get the mixture through the tip of the bag. You'll have to warm it up a bit first. This is also great on bagels or bialies.