In a large bowl, mix together the flour, corn starch and salt.
Gradually pour in the cold beer. Be careful not to overmix; a few lumps in the batter are fine.
Prepare the vegetables and/or seafood you plan to fry, patting them dry to ensure better adhesion of the batter.
Heat a generous amount of cooking oil in a deep fryer or large pot to 175-180°C (350-360°F).
Dip the prepared ingredients into the batter, ensuring they are evenly coated.
Fry the tempura in batches until they turn pale golden brown and crispy, about 2-3 minutes per batch. Avoid overcrowding the fryer.
Drain the fried tempura on a wire rack to maintain crispness.
Serve immediately for the best texture. The batter should be light, crispy, and complement the delicate flavours of the tempura.