• Gather all the ingredients.
  

To Prepare the Ingredients

• With a knife, cut off the stems of 2 okra but don‘t remove the entire top. Then, peel off the tough calyx around the top.
  
• Blanch the okra in a pot of boiling water for 2–3 minutes (or small okra for 1–2 minutes and large okra for 3–4 minutes). As soon as they are tender, drain in a sieve. Do not overcook. Slice crosswise into small pieces.
  
• Peel the skin of 1 Japanese or Persian cucumber in a striped pattern. Slice diagonally into thin oval slabs, then stack and julienne into matchsticks.
  
• Stack and tightly roll up 5 shiso leaves (perilla/ooba), then chiffonade crosswise into thin strips.
  
• Make a Japanese-style poached egg (onsen tamago) in the microwave. (For detailed instructions and step-by-step photos, see my 2-Minute Microwave Onsen Tamago recipe.) Crack 1 large egg (50 g each w/o shell) into a small, microwave-safe bowl. Pour in some water around the edges to push the egg to the center, then add just enough water on top to submerge the yolk. Puncture the yolk with a toothpick. Place in the microwave at the outer edge of the tray and heat at half power for 90 seconds or until the egg white just solidifies and turns white. Remove it from the water and transfer to a bowl.
  
• Discard the pit of 1 umeboshi (Japanese pickled plums), then chop the flesh.
  
• Open 1 package natto (fermented soybean) and add the sauce packet, umeboshi and shiso. Using chopsticks, mix it together really well. Tip: In Japan, they say to stir the natto 100 times. This incorporates air for a fluffy texture and releases the glutamate in the culture for improved umami.
  

To Assemble the Cold Natto Udon

• Bring water to a boil in a medium pot. Add 1 serving udon noodles and boil the frozen udon for 1 minute to heat through. Drain, then run the noodles under plenty of cold tap water to cool. If you‘d like, you can place the udon in cold water and add ice cubes to chill while you prepare the other ingredients.
  
• Make the sauce by combining 1 Tbsp mentsuyu (concentrated noodle soup base), 3 Tbsp water, and several ice cubes in a small jug with a spout.
  
• Transfer the cold udon to a plate. Add the okra, cucumber, onsen tamago, natto, and 2 Tbsp kimchi in neat piles on top of the noodles.
  
• Right before serving, peel and grate 1 inch nagaimo/yamaimo (mountain yam). I use a ceramic grater that I love. Note: The nagaimo may irritate your skin and cause itchiness. Work quickly and rinse your hands immediately after touching it or wear kitchen gloves. Nagaimo is very slimy and slippery, so make sure you have a good grip on it.
  
• Immediately pour the grated nagaimo onto the udon. Top with 1 tsp toasted white sesame seeds. Serve immediately. Pour the mentsuyu sauce onto the Cold Natto Udon at the table and enjoy.
  

To Store

• You can keep the leftovers in an airtight container and store in the refrigerator for up to 3 days and in the freezer for a month.