Before you start mixing, gather all your ingredients and utensils. Having everything within reach will make the process smoother. Ensure your sparkling water is chilled; colder ingredients yield a crispier batter!

In a mixing bowl, combine the cornstarch, all-purpose flour, salt, pepper, and baking powder. Whisk them together until they’re well-blended. The baking powder is key here; it helps create that lightness we’re after.

Once you have your dry mix, create a small well in the center. Add in the cold sparkling water and the slightly beaten egg. This bubbly water will add an extra layer of airiness to the batter.

Using a whisk, gently combine the ingredients until they just come together. Aim for a slightly lumpy texture—overmixing can lead to a denser batter, which defeats the purpose of tempura's airy crunch.

Now comes the fun part. Be sure to heat your oil to about 350°F (175°C). Dip your prepared ingredients into the batter, allowing any excess to drip off. Then carefully place them in the hot oil. Fry until golden brown, which usually takes about 2-3 minutes. Remove and place on paper towels to absorb excess oil.