Heat oil over medium-low heat until it reaches 340 to 360 degrees Fahrenheit. If you do not have a thermometer, look for oil that’s shimmering.

Whisk flour, cornstarch, baking powder and salt, then add seltzer and mix until just combined. The batter should be thin and resemble a pancake batter. Do not overmix!

Coat a small batch of vegetables into the batter, either piece by piece or all at once. Remove from the batter with a slotted spoon, allowing excess batter to drip off before dropping carefully into the hot oil. Take care not to crowd the pot, as this will lower the temperature of the oil, which will result in soggy tempura (and there’s nothing worse than soggy tempura!). While the first batch is frying, batter the next batch of vegetables. Once vegetables are golden and crispy, use tongs or a spider to transfer to a paper towel-lined baking sheet or cooling rack. Repeat with remaining vegetables.