Vegan Dashi Broth:
In a medium pot or bowl, add 2.5 cups water, kombu, and dried shiitake mushrooms. Steep for at least 30 minutes or overnight. Crispy Seasoned Eggplant:
Cut off the eggplant ends into roughly 2-inch wedges with skin-on. The skin will hold the shape together. Without the skin, the flesh will become too soft.
Soak them in water to remove astringency. Set aside for 15 minutes and dry them with a paper towel.
Coat the eggplant nicely with cornstarch.
Start frying the eggplant with oil in a large frying pan over medium-high heat . Do not touch too often. Only flip them when the bottom sides are nicely brown. If they stick to the pan, be patient and wait till the eggplant slice releases itself from the bottom when they form a nice crust. Reduce the heat to medium when eggplant turns golden brown and season it with mirin and soy sauce.
The cornstarch will thicken the sauce quickly, so flip around to coat the eggplant with the sauce. Then transfer to a plate.
Udon Soup Broth:
Transfer the kombu and shiitake dashi broth (including hydrated kombu) to the saucepan and bring it to a simmer.
Right before boiling, remove the kombu. With a fine-mesh simmer, skim off the foam and scum floating on the surface of the broth.
Add 1 Tbsp mirin, 1 tsp sugar, and 1 Tbsp soy sauce.
Add ¼ tsp salt and fried tofu. Turn off the heat and cover (so it won’t evaporate).
To Blanch Bok Choy, Cook Udon Noodles, and Assemble
In a large pot of boiling water, blanch the bok choy just until it turns bright green and tender, about 2 to 2.5 minutes, and transfer to a plate. I undercook slightly and so the remaining heat will continue to cook a bit more. For this recipe, I didn’t “blanch and shock” for retaining the vegetable color and crunch as I usually do since I wanted to keep the bok choy warm. Cook or reheat udon noodles according to the package instructions.
Drain udon noodles well and serve them in individual bowls. Divide and serve fried firm tofu and soup broth.
Top the noodles with blanched bok choy, minced mushrooms, and fried eggplant. Serve immediately with shichimi togarashi on the side for a spicy kick.