How to Make It
Place the noodles in a large bowl and cover with boiling water. Soak until the noodles have softened, at least 15 minutes.
Meanwhile, in a small saucepan set over medium heat, add the brown sugar, tamarind concentrate and fish sauce. Bring to a simmer and simmer gently until the brown sugar dissolves, about 1 minute. Drain the noodles using a strainer or colander.
In a wok or large skillet, heat 1 tablespoon of the oil over medium-high heat until it shimmers. Add the shrimp and cook, stirring constantly, until the shrimp is just cooked through, about 1½ minutes. Transfer the shrimp to a plate. Add the remaining tablespoon of oil to the wok and when hot, add the shallots and cook, stirring often, until they turn translucent and begin to brown, about 1 minute. Turn the heat to medium-low, add the eggs and stir quickly to mix the yolks and whites. Continue cooking, while stirring, until the eggs are just set, about 30 seconds. Add the noodles, return the heat to medium-high, and cook, stirring constantly, until the noodles are warmed through, 30 seconds to a minute. Add the reserved shrimp, then add the prepared sauce and cayenne and cook, stirring, until the noodles and chicken are coated. Add the bean sprouts and cook, stirring, until the bean sprouts are barely wilted, about 30 seconds. Taste the noodles. Adjust the seasoning, if needed.
Transfer the pad Thai to two bowls. Garnish with the peanuts and serve with lime wedges.