Tororo Soba

To prepare dashi stock, gently wipe Kombu with a damp cloth. Place Kombu in a pot with 500 grams of water and let it soak for 30 minutes. Heat the pot over medium-low heat. Just before the water boils, remove the Kombu. Bring the water to a boil, then turn off the heat and add Katsuobushi. Let it steep for 30 seconds, then strain the dashi stock through a fine-mesh sieve, discarding the Katsuobushi. You should have approximately 400 grams of dashi stock.

For the tsuyu sauce, combine Mirin and Sake in a small saucepan. Bring to a boil over medium heat to evaporate the alcohol, about 30 seconds. Reduce heat to low, then add the 400 grams of dashi stock, Koikuchi soy sauce, and Sugar. Simmer for 1 minute, then remove from heat and let the tsuyu cool.

Carefully peel the Nagaimo. Using an oroshigane (Japanese grater) or a fine grater, grate the Nagaimo into a smooth, sticky paste. Set aside.