Wash the asparagus and cut off the woody ends. Cut thicker stalks in half lengthwise. Mix rice flour, baking powder, egg, mineral water and 1⁄2 TL salt briefly to a viscous dough. Let rest for 30 minutes.
For the sauce, wash the chervil, shake dry and chop finely. Puree with horseradish, vinegar and sugar. Fold in olive oil. Season to taste with salt and pepper.
Heat the frying fat in a deep fryer or a wide pan. Pull asparagus spears individually through the dough and deep-fry them in portions in hot oil for 2-3 minutes until crispy. Drain on kitchen paper.
Sort the Mizuna or rocket, wash and shake dry. Arrange asparagus tempura with salad and chervil sauce.