Add the flour, cornstarch, baking powder, and salt to a large bowl and stir until well combined.

Add the sparkling water gently, while you're whisking until well combined, but don't over-mix. You can use a whisk, a fork or your chopsticks. Set aside.

Dip veggies into the batter, one at a time, to lightly coat, shaking off any excess batter.

Pour the oil into a saucepan, wok, pot or a deep skillet and when it's hot, add the veggies. Cook for 1-2 minutes. Flip and cook 1-2 minutes on opposite sides. You could also use a fryer, but I prefer this method.

To make your tempura extra crispy and extra beautiful, dip your chopsticks into the batter and just pat on the veggies. Repeat a few times on each piece of tempura. This step is optional.

Don't add too many veggies at the same time or the temperature of the oil will drop and your tempura will go soggy. I usually add 4, but the number may vary depending on the size of your veggies. If you want to save time and you don't mind getting a better result, just add as many veggies as you want.

Transfer the veggies to a cooling rack, that way they won't go soggy, and also they will be less greasy. You can also use a paper towel, but the rack works amazing and is also zero waste.

To make the sauce, just mix all the ingredients in a saucepan, bring to a boil and simmer for 5 minutes.

You can keep the sauce in an airtight container or a jar in the fridge for at least 1 week. The tempura is best when fresh, but you can keep the leftovers in an airtight container in the fridge for 3-4 days. The sauce is optional, but your tempura pieces will taste much better if you dip them into the sauce.