how to make tempura flakes at home - 1/2 cup of flour, 1/2 cup cornstarch, 1 cup of water seltzer (club soda or other bubbly water), 1 egg and a pinch of salt. * Don't over-stir, few lumps are expected. * Only use a very cold liquid * Prep everything and make your batter last. Keep it chilled while frying. Oil at temperature to 170 and 180 degrees.