Put the salmon, cream cheese, and mascarpone in a small, shallow bowl and mash them together with a fork until just combined. Add the lemon zest, lemon juice, and dill and season well with salt and cayenne. Mash again until well blended. Taste and adjust the seasoning to balance the filling nicely.
Lay a crêpe presentation-side down on a clean work surface and gently
spread with one-quarter of the filling, taking care not to rip the crêpe
as you spread. Neatly roll the crêpe into a tight cylinder, and then
transfer it to a large plate. Repeat with the remaining crêpes and
Wrap the plate of crêpes in plastic and refrigerate until the filling is firm, at least 30 minutes or up 8 hours.
ready to serve, cut each crêpe crosswise on the bias into bite-sized
pieces, so that one side of each piece is flat and the other side is
angled. Arrange the crêpes on a serving tray or platter so they’re
standing on the flat side, with the angled side pointing up, and garnish
each piece with a small sprig of dill. Serve chilled.