Heat a wok over medium-high heat. When hot, add 2 tbs oil, then the shrimp. Cook the shrimp just until cooked through, stirring constantly. Remove to a bowl. Add the remaining 2 tbs oil, then lower the heat to medium. Add the tofu, shallot, garlic, dried shrimp, and serrano. Cook, stirring, until the tofu is heated through and the shallot starts to wilt, about 2 minutes. Push the veggies to one side, then add the beaten egg to the space you made. Don’t touch for about 10 seconds, then basically scramble them for about a minute, maybe less. When they are almost set, quickly stir them in with the tofu mixture. Immediately add the noodles and shrimp, then the fish sauce mixture. Stir vigorously until everything is coated with the sauce. Remove from the heat. Taste and adjust the fish sauce and tamarind concentrate as necessary. If using, add your bean sprouts here and toss to combine.