• Gather all the ingredients. Bring a large pot of water to a boil. Prepare a large bowl of cold water with ice cubes.
  

To Make the Sauce

• Even though your sesame seeds are pre-toasted, we will freshly toast them now to enhance their nutty aroma. Add 3 Tbsp toasted white sesame seeds to an ungreased frying pan and turn on the stove to medium-high heat. Once the pan is hot, lift it up and shake it constantly over the flame. Toss and turn over the sesame seeds in the pan to evenly toast them. When they are fragrant, turn off the heat and move the pan off the stove.
  
• Transfer the toasted sesame seeds to a mortar (suribachi). Grind them with a pestle (surikogi). Leave some seeds whole for texture.
  
• To the ground sesame seeds, add 1 Tbsp soy sauce and 1 Tbsp sugar and mix it all together. Set aside.
  

To Cook the Spinach

• Once the water is boiling, add 1 tsp Diamond Crystal kosher salt. Add 1 bunch spinach to the boiling water, stem side first, and cook for 20 seconds, as the stems take longer to cook.

  Nami's Tip: Salt helps keep the spinach's green color brighter.
  
• Then, gently push the leafy part into the water and cook for 30–45 seconds.

  Nami's Tip: Spinach in the US is more tender than Japanese spinach, so it cooks faster.
  
• Transfer the spinach from the pot and plunge it into the iced bath to stop the cooking for 1 minute.

  Nami's Tip: Blanching and shocking in ice water removes much of the oxalic acid, locks in nutrients, and keeps the spinach vibrant. Do not leave it for more than a minute, or it will start to lose nutrients.
  

To Assemble

• Once the spinach is cool enough to handle, collect the spinach and squeeze the water out. Tip: Do not leave the spinach in the water for too long or else it will lose nutrients.
  
• Cut the spinach into 1-inch (2.5 cm) lengths and put it in the mortar. If your mortar is small, transfer the sesame dressing and spinach to a bowl.
  
• Toss it all together. Serve at room temperature or chilled.
  

To Store

• You can keep the leftovers in an airtight container and store in the refrigerator for 2–3 days or freezer for 2–4 weeks.