Press the tofu to remove excess water. You can do this either with a tofu press, or by wrapping the tofu in a clean kitchen towel and placing it on a wire rack suspended over a baking pan with a can or heavy object on it for 30 minutes. Freeze the pressed tofu in a container for at least 4 hours.
Thaw the tofu while continuing to press it again to get rid of additional moisture.
Tear the tofu into slightly larger than bite-sized pieces.
In a mixing bowl, combine the garlic, ginger, tamari, sake, and sugar to prepare the marinade. Drizzle the tofu pieces to the marinade, and very gently move them around to ensure they are evenly coated. Cover and refrigerate for 4 hours or overnight.
In a separate bowl, whisk the plant-based milk with rice vinegar to create a curdled mixture. Place the potato starch, and if you are using it, the togarashi, together in another bowl. Dip each piece of marinated tofu into the curdled milk mixture, allowing excess to drip off, then coat thoroughly with potato starch.
Heat oil in a dutch oven, or wok over medium heat to 350°F (175°C). Fry the coated tofu pieces in batches until golden brown and crisp, turning occasionally for even cooking. Remove and place on a wire rack to drain excess oil.
Alternatively, preheat an air fryer to 375°F (190°C). Arrange the coated tofu in a single layer in the air fryer basket, ensuring there is space between pieces. Cook for 10-12 minutes, shaking the basket halfway through, until crispy and golden.
Arrange the tofu karaage on a serving plate and garnish with cucumber slices, julienned radish, and thinly sliced scallion. Sprinkle with shichimi togarashi if desired. Serve immediately.