Soak in water for 10 minutes:
eggplant, sliced to your liking (3cm rounds, slices, whatever)
Remove from water and pat dry.
While the eggplant is soaking, mix the tempura batter:
⅓ C white flour
⅓ C cornstarch
⅓ C sake
enough ice water so the batter is the consistency of a thick white sauce
(The colder the batter, the crispier the tempura. Sometimes I mix in ice cubes until the correct consistency is reached.)
Heat in a heavy-bottomed pan:
When a drop of tempura batter placed in the oil bubbles and comes up to the surface immediately, the oil is hot enough. The oil should remain 170º-180ºC (340º-360ºF) throughout, so be careful not to add too many pieces at the same time as that will reduce the oil temperature.
Dip the eggplant pieces one at a time in the batter and deep fry until golden. Drain over newspaper. (Pat off excess oil with a paper towel.) Arrange on a serving plate.
Make the sauce in a microwave safe bowl:
1 t finely grated ginger
1 t finely grated garlic
¼ C soy sauce
¼ C mirin
1½ T sugar
1 t tobanjan (Chinese hot chili sauce)
2 T apple cider vinegar
Heat for 30-60 seconds in the microwave. Add:
1 T minced green onion (negi)
Pour over cooked eggplant. Serve.
This sauce can also be used for as a topping for tofu, fried fish, fried chicken, spring rolls, etc.