Soak the noodles in a large bowl of cold water for 20 minutes until they become soft and pliable, then rinse them of any starch under cold running and drain well.
In a bowl, stir together the sugar, tamarind water, vinegar and fish sauce until the sugar has completely dissolved. This is your pad thai seasoning sauce. Set aside.
In a pestle and mortar, pound the shallot, garlic and salt together to a coarse paste. Heat the pork fat or vegetable oil in a large wok over a medium heat, then add the paste and fry for 1 minute until fragrant and beginning to brown.
Crack the egg into the hot fat and stir so that the yolk breaks. Cook for 20-30 seconds until the egg resembles a soft omelette.
Add the drained noodles and stir to break up the egg, distributing it among the noodles. Add the seasoning sauce, along with the diced tofu, dried shrimp, shredded salted radish
and crushed peanuts. Stir and toss all the ingredients well, then leave to simmer for 1 minute until almost all the sauce is absorbed and the noodles are completely tender.
Add the bean sprouts and spring onions, then toss and stir one final time so that all the ingredients are well combined and distributed. Transfer to serving plates and sprinkle with some more bean sprouts.