Drain the 14 oz extra-firm tofu and press it for at least 20–30 minutes to remove excess moisture. After pressing, slice the block into 6 even slabs about 1/2 inch (1.2 cm) thick. Pat the slices dry with paper towels and season both sides lightly with 1 tsp salt and 1/2 tsp black pepper.

Make the batter

In a medium bowl whisk together 3/4 cup all-purpose flour, 1/4 cup cornstarch, and 1/2 tsp baking powder. If using the egg, beat it lightly and add to the dry mix. Pour in 1/2 cup cold sparkling water and whisk to a smooth, slightly thick batter — it should coat a spoon but still be fluid. Adjust with a tablespoon more water or flour if needed.

Heat oil

In a large nonstick or stainless skillet, add about 4 tablespoons vegetable oil and heat over medium-high until shimmering (about 350°F/175°C if using a thermometer). There should be enough oil for shallow frying the tofu (about 1/8–1/4 inch depth).

Batter and fry tofu

Working in batches, dip each tofu slab into the batter, letting excess drip back into the bowl, then place gently into the hot oil. Fry 2–3 minutes per side until the batter is golden and crisp. Use tongs or a spatula to turn carefully. If the oil browns too fast, lower the heat to medium. Transfer cooked tofu to a wire rack or paper towels to drain. Repeat for remaining slices, adding up to 1 tablespoon oil between batches if needed.

Finish

If desired, brush each fried tofu steak very lightly with 1/2 teaspoon toasted sesame oil for aroma. Sprinkle with 1 tablespoon toasted sesame seeds and sliced green onions (2 stalks thinly sliced).

Homemade Teriyaki Sauce

Combine sauce ingredients

In a small saucepan combine 1/2 cup low-sodium soy sauce, 2 tablespoons mirin, 1 tablespoon sake, 2 tablespoons brown sugar, 1 tablespoon honey (or maple), 1 teaspoon grated fresh ginger and 1 minced garlic clove. Stir to combine.

Simmer and reduce

Bring the mixture to a low simmer over medium-low heat. Let it simmer gently for 3–4 minutes to meld flavors and dissolve the sugar.

Thicken sauce

Mix 1 teaspoon cornstarch with 2 tablespoons cold water to make a slurry. Whisk the slurry into the simmering sauce and cook 1–2 minutes until the sauce thickens to a glossy, pourable consistency. Remove from heat. Taste and adjust sweetness or salt; add a splash of water if too thick.

Finish sauce

Optionally stir a few drops of sesame oil for aroma. Keep warm until ready to serve.

Serve

Arrange the battered tofu steaks on a warm platter and spoon the teriyaki sauce over each piece or serve sauce on the side for dipping. Garnish with extra sliced green onions and toasted sesame seeds.