Although this Bluefin Tuna Tartare sticks closely to the classic French recipe for steak tartare, the raw egg yolk has been replaced with a wasabi espuma for a novel modern twist on the original. Parsley juice infused with wasabi and thickened with raw egg whites, the mixture is charged with nitrous oxide in a siphon to turn it into a light-as-air foam. Served atop a mound of silken cubes of tuna seasoned with capers, onions and mustard, this simple appetizer looks far more involved than it actually is.