Prepare

Preheat the oven to 400°F (200°C).

Line a 1-quart (1-liter) terrine mold or a 9 by 5-inch (23 by 12-cm) loaf pan with plastic wrap, with a generous overhang around the edges.

Trim the root end and the dark green tops off the leeks. If they’re very large, cut them in half lengthwise. Rinse them very thoroughly until all sand has been washed off. Place them on a parchment paper–lined baking sheet. Roast the leeks for about 30 minutes, or until brown and very tender. Let cool.

If using powdered gelatin, sprinkle it over ¼ cup (60 ml) cold water in a cup and let stand until softened, 5 to 10 minutes. (Soak gelatin sheets in a bowl of cold water until softened, then drain and squeeze out the excess water.)

In a saucepan, heat the mascarpone over low heat, stirring, then add the soaked gelatin and stir to dissolve. Immediately remove the pan from the heat and beat in the cream cheese. Generously season with salt and pepper.

Peel off and discard the leeks’ outermost layers so only the soft cores remain. Use the widest leaves to line the bottom and sides of the terrine mold; press them a little to flatten if necessary, overlapping them slightly, like roof tiles. Allow the ends to hang over the edge a little.

Spread one-third of the mascarpone mixture on top of this bottom layer and cover with leeks, a layer of salmon, and whole chives. Repeat with another third of the mascarpone and continue layering until you have used up all the ingredients. Fold over the overhanging leek leaves and then cover with the plastic wrap. Place in the fridge to firm up at least 8 hours or overnight.

Make

Remove the terrine from the fridge about 1 hour before serving. Unfold the plastic covering the top and invert the terrine onto a cutting board. Lift off the mold and remove the rest of the plastic wrap. Use a sharp, warm knife to cut your terrine into gorgeous slices. Arrange them on a platter, sprinkle with crushed peppercorns if you wish, and serve.