Wrap the tofu in a clean tea towel, then firmly press to remove any excess moisture.
Cut the tofu in half horizontally.
Mix the soy, rice vinegar mirin and sesame oil in a bowl. Pour this into a freezer bag then add the tofu and move it around to coat. Close the bag and marinate for at least 30 minutes, turning the bag frequently to coat all sides of the tofu.
Take the tofu out of the marinade and remove the excess moisture by paper towels.
If you’re using egg - put this in a bowl and gently whisk. For a vegan version, pour the marinade into another bowl and add 1 spoonful of cornflour. Scatter the sesame seeds onto another plate.
Dip one block of the tofu in the egg or marinade mixture, coating the entire piece. Then put it into the sesame seeds, turning and pressing to coat on all sides. Repeat with the other piece.
Heat some oil in a heavy-based frying pan. Once hot, add the tofu blocks and cook over medium heat for 2-3 minutes on each side, until golden-brown.
Transfer the tofu to a plate lined with paper towel.
When the tofu has cooled cut the block into 5 mm thick slices. Serve with spring onion scattered over and some dipping sauce of your choice.