For the tempura dough, mix 1/4 l ice-cold water, 1 teaspoon salt, flour and starch. Stir in egg. Cover the dough and chill for about 30 minutes.
Wash and peel the asparagus and cut off the woody ends. Cut the asparagus in half lengthwise and crosswise. Mix mayonnaise and asia sauce for the dip. Season with salt, chilli powder and lemon juice.
Heat the frying oil in a high pan or a wide pot to approx. 180 °C (it is hot enough if small bubbles rise from a wooden skewer). Pull the asparagus individually through the tempura dough and fry in portions in the hot oil for 2-3 minutes until golden brown.
Drain on kitchen paper. Serve with the mayonnaise. Serve with green salad.