from the archives of rec.food.cooking, search--tempura.
http://www.neosoft.com/recipes

Make the tempura batter by whisking flour, cornstarch, baking powder, salt
in a medium bowl and whisking in egg whites and beer. Let sit in the
refrigerator about 30 minutes.

Pour peanut oil into a deep saucepan to the depth of about three to four
inches and heat on high until a bread cube dropped into the oil immediately
sizzles.