Step 1Cut 4-inch pieces from the tip of the asparagus and set aside remaining pieces for another use. Wash the asparagus well in cold water. Dry completely.
Step 2In wide shallow bowl, whisk together the egg, 1 cup flour, salt, cayenne pepper and club soda.
Step 3Pour oil to a depth of about 3 inches in a deep heavy saucepan. Heat to 360 degrees.
Step 4Dredge the asparagus spears in flour, shaking off excess, then in batter. Working in batches, lay the asparagus into the hot oil and fry just until golden brown and crisp, turning to brown all sides, about 2 minutes. Transfer to a platter lined with paper towels and sprinkle with additional salt. Serve hot, with ponzu or tempura dipping sauce if desired.