02To make the butter (up to 3 days ahead): Using a mortar and pestle or the side of a knife, mash the garlic with a pinch of salt until it forms a paste. Transfer to a bowl. Add the butter, 1 tablespoon of fennel fronds, tarragon, orange zest and pepper. Stir to combine.03To serve, spread fennel-orange butter on slices of pumpernickel. Wipe off most of the marinade from the salmon and slice off the skin. Thinly slice the fish, pile it on the pumpernickel, and sprinkle with salt, more black pepper and a little lemon juice. Top with fennel fronds.