1. Lightly grease a small loaf pan, bowl, or mold with neutral oil, or line it with plastic wrap if you plan to unmold the mousse for serving. Set aside, and chill a medium mixing bowl for whipping the cream.

2. Sprinkle the unflavored powdered gelatin evenly over the cold water in a small heat-safe bowl. Let it sit for 5–10 minutes, without stirring, until the gelatin absorbs the water and looks thick and spongy.

3. Gently warm the bloomed gelatin over a pan of simmering water or in very short microwave bursts, stirring just until the gelatin is fully dissolved and fluid. Set aside to cool slightly while you prepare the salmon mixture.

4. In the bowl of a food processor, combine the chopped smoked salmon, softened cream cheese, Greek yogurt or sour cream, lemon juice, lemon zest, Dijon mustard, sea salt, and black pepper. Process until the mixture is completely smooth, pausing to scrape down the sides of the bowl as needed.

5. With the processor running on low, slowly pour in the warm, dissolved gelatin and blend just until it is fully incorporated into the salmon mixture. Do not let the gelatin get too cool or it may start to set before it’s mixed in.

6. Add the chopped dill, chives, and capers (if using) to the processor. Pulse a few times to distribute them evenly while still keeping small green flecks visible throughout the mousse. Taste and adjust seasoning with additional lemon juice, salt, or pepper as desired.

7. In the chilled mixing bowl, whip the cold heavy cream with a hand mixer or stand mixer until soft peaks form. The cream should hold its shape but the tips should gently fold over when you lift the beaters.

8. Transfer the salmon mixture to a large mixing bowl. Gently fold in about one-third of the whipped cream to lighten the base. Then fold in the remaining whipped cream in two or three additions, using a spatula and broad, gentle strokes so you don’t deflate the mixture.

9. When the mousse is smooth and uniformly pale, spoon or pipe it into your prepared serving dish or mold. Smooth the top with a spatula and tap the dish lightly on the counter to release any large air pockets.

10. Cover the dish tightly with plastic wrap and refrigerate for at least 2 hours, or until the mousse is chilled through and softly set. For the best flavor and structure, chill for 4 hours or up to overnight.

11. When ready to serve, if you used a mold, run a thin knife around the edge and briefly dip the bottom of the mold in warm water before inverting onto a serving plate. Garnish with extra dill, chives, lemon zest, or small pieces of smoked salmon.

12. Serve the mousse well chilled with crackers, toast points, baguette slices, cucumber rounds, or crisp vegetable sticks. Refrigerate any leftovers promptly and enjoy within 2–3 days.