• Gather all the ingredients.
  
• Peel the skin of 1 Japanese sweet potato (Satsumaimo) alternately to create stripes. Then, cut and discard both ends.
  
• Cut the sweet potato into rounds about ½-inch (1.3-cm) thick. Soak them in water for 5 minutes to remove the starch, then drain.
  
• In a medium saucepan, add 1 cup water, 2 Tbsp sugar, and juice from ½ lemon.
  
• Add the sweet potato rounds in a single layer (ideally) in the saucepan and place an otoshibuta (drop lid) on top instead of the regular lid (here‘s why). Bring it to boil over medium heat.
  
• Once boiling, skim off the scum and foam with a fine-mesh skimmer. Turn down the heat to simmer/low heat. Cook for 15–20 minutes.
  
• When it’s almost done, open the otoshibuta and insert a bamboo skewer in the center of the thick sweet potato and see if it goes through.
  
• Turn off the heat when it’s done cooking, and serve. Ideally, set aside and let cool for 2 hours so sweet potatoes can absorb more flavors. You can chill the sweet potatoes in the refrigerator before serving or serve at room temperature.
  

To Store

• You can keep the simmered sweet potatoes in the refrigerator for up to 5 days. You can freeze them, but the texture of the sweet potatoes will change slightly.