Drain the firm tofu, wrap it in kitchen paper, place it on a microwave-safe plate, and microwave at 600W for 2 minutes without covering. Remove excess water and let it cool.

Cut the tofu into 4 equal pieces and coat all sides with potato starch.

Heat salad oil in a frying pot to 170°C. Fry the tofu pieces for about 3 minutes, turning them until golden brown and crispy. Drain the oil and place the tofu on a serving plate.

In a saucepan, combine water, dashi powder, mirin, and soy sauce. Heat over medium heat until it starts to simmer, then turn off the heat to make the sauce.