First make the curry paste. Beginning with the salt and bird's eye chilies, use a pestle and mortar to work the chillies into a powder. Then add the lemongrass and repeat until you're left with a smooth paste. Move down the ingredients list, pounding each ingredient until smooth before adding the next.
Heat a pan to medium and add the oil. Fry the tofu and mushroom for a few minutes before adding the curry paste. Stir fry slowly, incorporating the curry paste with the tofu and mushrooms. Cook, stirring often, for about ten minutes.
Season with soy sauce and sugar, stirring until mixed through. Add the makrut lime leaves, fresh green peppercorns, and sliced long red pepper. Cook for a couple more minutes. Taste and season as you go – you may need more salt and/or soy sauce, depending on whether or not you used vegan shrimp paste in your curry paste (and on the various degrees of salt that ingredient could have if you did).
Serve warm or at room temperature with jasmine rice and fresh vegetables like sator bean (stink bean), cucumber, lettuce, cabbage, and pennywort leaf. While unusual in Thailand, carrot is also a great accompaniment.