Take 450 g kabocha squash and scoop out the seeds and stringy fibers thoroughly with a strong metal spoon.
Use a sharp strong knife to cut the kabocha into chunks, making sure each piece has some skin attached. If your kabocha is too hard to cut, try microwaving it for 2-3 minutes before cutting.
Optional step: With your knife or a peeler, shave the edges of each wedge. This is called mentori and will prevent breaking and improve presentation.
Arrange the kabocha in a wide pot in a single layer with the skin side facing down. Add 300 ml dashi stock, 2 tbsp mirin, ½ tbsp sugar and 2 tbsp sake. Bring to a boil over medium heat and let it bubble for 2 minutes.
Measure out 2 tbsp Japanese soy sauce (koikuchi shoyu), then after 2 minutes of boiling, pour about two-thirds of it into the pot.
Reduce the heat to a gentle simmer and cover the kabocha with a drop lid (or circle of parchment paper/foil). Simmer for 10 minutes or until the kabocha is soft enough to pierce with a fork. Then turn off the heat, and add the rest of the measured soy sauce.
Optional cooling step for best flavor (recommended): With the drop lid still in place, move the pot to a trivet on the counter and cool to room temperature.
Reheat gently over low heat, or serve cold according to preference. Enjoy!
Notes
Soy sauce goes in twice. Add roughly two-thirds at the start of simmering for depth and salt penetration. Stir in the remaining third after you turn off the heat to preserve the fresh aroma. A single addition loses the bright top notes that make the dish layered.Cooling is the real cooking. Leave the pot undisturbed for at least 30 minutes after the heat goes off. The kabocha draws the seasoned broth inward as it cools. Taste a piece at 10 minutes and again at 30, and you will understand why. Overnight in the fridge is ideal.Drop lid sits on the food. Place a circle of parchment paper (with a small center hole) or aluminum foil directly on the kabocha, not on the pot rim. This creates steam recirculation that bastes the exposed surfaces evenly.No dashi? Use water. Plain water with the soy sauce, mirin, sugar, and sake still makes a good dish because kabocha releases starch and sugars that give the broth body on its own. It just wouldn't have as much umami and depth.