How to Make It
In a bowl, whisk 3/4 cup of the all-purpose flour with the rice flour, 1 1/2 teaspoons of salt and the baking soda. Whisk in the beer and vodka until the batter is very smooth. Strain the batter, then pour it into the canister of a 1-pint iSi Gourmet Whip Plus siphon. Seal the siphon and charge it with one iSi cream (N20) cartridge according to the manufacturer’s instructions. Shake the siphon to distribute the gas. Repeat with a second cream cartridge.
In a large saucepan, heat 2 inches of oil to 350°. Put the remaining 1 cup of all-purpose flour in a shallow bowl. Dredge the onion rings in the flour. Working in 3 to 4 batches, shake off the excess flour and transfer the rings to a large bowl. Holding the siphon upside down, carefully press the handle to dispense just enough batter to coat the rings. Using tongs, lift the onion rings from the batter, allowing any excess to drip off, and carefully transfer them to the oil. Fry the onion rings until they are golden brown and puffed, about 3 minutes per batch. Drain on paper towels and season lightly with salt. Repeat with the remaining onion rings and batter; serve hot.
The 1-pint iSi Gourmet Whip Plus is sold on amazon.com for $109; 24 cream (N20) cartridges are $17.