Use a food slicer to cut 8 thin slices of wild salmon, previously frozen, the same size as the bread. Season.
Sear the salmon very quickly on the griddle on one side only.
Slice the mozzarella.
On a slice of bread, lay 2 slices of salmon, 1 slice of mozzarella, the chopped truffle and a drizzle of truffle oil, and finish with another slice of bread to make a sandwich. Cut into 4 quarters.
Spread the outer sides of the bread with butter and sear on the griddle like a toasted sandwich.