• Gather all the ingredients.
  
• Cut ½ sweet onion in half with the root end intact. This helps hold the layers of the onion together while grating or mincing.
  
• Grate half the onion. I use my favorite ceramic grater to collect the onion juice. Onion juice is an important ingredient for the dressing, so make sure to collect all of it.
  
• Finely mince the remaining half of the onion (we call this Japanese cutting technique mijingiri). Lay the onion flat side down on the cutting board. With the knife edge toward the root end, make ⅛-inch horizontal slices to within ½ inch of the root end to keep it intact. Then, with the knife tip pointing toward the root end, make ⅛-inch vertical slices to within ½ inch of the root end. Finally, make perpendicular cuts down through the vertical slices you made.
  
• To mince the onion even finer, run your knife through the onion pieces using a rocking motion while holding down the tip of the knife.
  
• To a mason jar, add both the minced onion and the grated onion with all the onion juice.
  
• Add 4 tsp sugar, 1½ Tbsp soy sauce, ¼ cup extra virgin olive oil, and 3 Tbsp Japanese black vinegar (kurozu).
  
• Shake to combine and dissolve the sugar. Refrigerate overnight (8–12 hours) or longer to meld the flavors. The flavors of the dressing significantly improve after resting.
  

To Serve

• Make the optional green salad. Here, I simply toss together frisée and radicchio, thinly sliced watermelon radish, and heirloom tomatoes in a salad bowl. Drizzle the Japanese Onion Dressing on top, toss, and serve.
  

To Store

• You can keep the dressing in an airtight container and store it for 7 days in the refrigerator.