Dried shrimp and tamarind concentrate. We ate pad thai three times this month and I can confidently say that this recipe from Nongkran Daks is the best I've ever tried. She lists the dried shrimp as optional, but I went ahead and included it when I made the sauce. But first, you have to pound them up into a nice, fluffy shimp powder.
I tried several ways of preparing tofu for pad thai and this is my favorite. It takes some extra steps, but the texture is perfect. First, freeze a block of extra firm tofu and then defrost. The texture will have become crumbly, sort of like ground beef. Drain as much of the moisture as possible and then cook in a hot pan with a bit of oil until browned. Do this while cooking down the sauce to the consistency of molasses. (The best thing about this recipe is that you can make the sauce and soak the noodles ahead of time and then throw the pad thai together in just a few minutes.)
Once the tofu is browned, add the drained noodles you have been soaking and a bit of water. Keep adding water and cooking it in until the noodles are the texture you are looking for. This is the step that I have missed in the passed and the way to get perfectly chewy - not crunchy - noodles. I've made this with and without the egg and it is good either way. Then you toss with the sauce, mung beans, and some peanuts. The key to keeping the pad thai from being too soupy (a common problem with my previous attempts) is to use this concentrated sauce and work in small batches with a hot pan. Enjoy!!!
Think you have a better pad thai recipe? Please link to it in the comments - I'm always looking to improve!