6 ounces Thai or Vietnamese medium-width flat rice noodle (sen lek or banh pho)
1/4 cup Thai or Vietnamese fish sauce (nam pla or nuoc nam)
1/4 cup tamarind concentrate or homemade tamarind water (see Note)
2 tablespoons palm sugar, or 1 1/2 tablespoons brown sugar
1 teaspoon Asian chili paste, such as sambal oelek, plus more for serving
4 tablespoons vegetable oil
1/4 cup coarsely chopped shallots
3 ounces pressed tofu, cut into 3/8-inch cubes or batons that measure 1/4-inch thick by 1-inch long
2 teaspoons finely chopped preserved radish (hua chay poa, aka preserved turnip), rinsed (optional)
2 tablespoons dried baby shrimp, softened in hot water for 5 to 20 minutes if hard, (optional)
6 ounces boneless chicken breast, thinly sliced into pieces 1 to 2 inches in length
3 tablespoons crushed unsalted roasted peanuts, plus additional for garnish
1 1/2 cups mung bean sprouts, plus more for garnish
1 small handful Chinese chives or green onion tops cut into 3/4 –inch lengths (about 1/2 cup)
Lime wedges, for garnish
1. Bring 2 to 3 quarts of water to a boil in a large pot. Put the noodles in a large bowl and cover with abundant boiling water. Let noodles soften until tender but still a bit firmer than you’d want to eat them, stirring occasionally, for 5 to 10 minutes depending on the brand (don’t overcook; test noodles early and often). Immediately drain in a colander and rinse thoroughly under cold running water. Set aside.
2. Put the fish sauce, tamarind, sugar, and 2 tablespoons water in a small saucepan and bring to a simmer, stirring to dissolve the sugar. Let simmer for 1 minute. Remove from the heat and taste the mixture: it should be salty, sour, and just slightly sweet; adjust with small amounts of each ingredient as needed. Stir in the chili paste and transfer the sauce to small bowl and reserve. The dish can be made up to this point a few hours ahead. Before beginning to cook, have all ingredients prepared, at room temperature, and close at hand.
3. Heat a 14- to 16-inch wok over medium-high heat for 2 to 3 minutes. Add the oil, swirling to coat wok. Add the shallots and cook, stirring, until beginning to brown, for a few seconds. Add the tofu (and radish and shrimp, if using) and cook, stirring frequently, until tofu begins to brown at edges, less than 1 minute.
4. Increase the heat to high and add the chicken. Cook until nearly cooked through, a minute or so, stirring frequently. Add the rice noodles and cook, stirring almost continuously until heated through, another minute or so.
5. Clear a space on one side of the wok. Working quickly, crack the eggs into the wok and roughly scramble and toss with the noodles for a few moments. Add the reserved sauce and toss to combine. Add the peanuts, bean sprouts, and chives, stirring and tossing to incorporate all the ingredients. Divide between plates and garnish with lime wedges and additional bean sprouts, peanuts, and chili paste.
Note: Tamarind concentrate is available at most Asian markets and works well in pad thai. However, it is a convenience product intended to stand in for the real thing: homemade tamarind water. Tamarind water - a thin paste made from tamarind pulp (also found at Asian markets) - is easy to make and tastes superior to concentrate. Here’s how: Cover a small portion of tamarind pulp with an equal amount of warm water and let soak for a few minutes to soften. Work the pulp with your fingers to help dissolve the paste and separate it from the seeds within. Strain the mixture, pushing on the mass of solids to release the pulp and leave the seeds behind. You should be left with a slightly fluid paste.