Tuna with Elderflower Buttermilk Foam

Place tuna in a plastic bag; add soy sauce, sake, and mirin. Seal; let tuna marinate, turning once, at room temperature for 30 minutes.

To make the foam, warm the elderflower liquor and buttermilk in a saucepan using medium heat. Add the gelatin powder and mix until completely dissolved and set aside.

Remove the dispenser from the box including the charger holder and two dispenser tips. Unscrew the top off the dispenser, then screw on the tip of your choice (straight or tulip) while holding in place the valve stem under the cap. Be sure to screw the tip on tightly. Make sure that the gasket (also called the O-ring) is firmly in place on the underside of the head.

Pour the foam liquid mixture it into the siphon of the dispenser. Do not exceed recommended amount. Screw the top evenly and firmly onto the bottle. Do not cross-thread. Place a n2o cartridge in the holder with the small end visible. Twist charger holder onto head until gas is released. A slight hissing sound will be heard. For a pint dispenser, use only one charger per filling. For a quart dispenser, use two chargers per filling.

Shake the dispenser 3-6 times. Turn the dispenser upside down. This is important, otherwise gas will escape and a proportionate amount of foam will not be released. To assemble the dish, plate the tuna on a serving platter and dispense foam on top as needed by pressing on the lever. Top the dish with sliced scallions and a sprinkling of fennel salt if desired. If the mixture is too runny, shake the dispenser a few more times and try again. If desired, the holder can be removed along with the used charger and the small cap put in its place.