Cut squash in half, remove seeds and cut in half. Peel skin using a sharp knife. To make it easier to cut and peel, place the whole squash in the microwave for a 1-2 minutes. Cut squash into 2 inch pieces.
Place dashi, soy sauce, sugar, mirin and squash in medium saucepan. Bring to a boil, then reduce heat and simmer on low for 10-15 minutes until squash is soft and cooked through.
Adapted from The Poetical Pursuit of Food by Sonoko Kondo.