Gather the ingredients. The Spruce

Make the sauce by combining sauce ingredients together in a cup. Stir well to dissolve tamarind and brown sugar. Taste-test for a tangy balance between sweet and sour. Add more sugar if too sour, or more tamarind if too sweet. The Spruce

Bring a large pot of water to boil and dunk in rice noodles. Stir to separate. Only cook until they are soft enough to be eaten, but just barely: still firm and a little "crunchy" (they will finish cooking later in the pan). The Spruce

Drain the noodles and rinse well with cold water to prevent sticking. Set aside. The Spruce

Place chicken slices in a small bowl. Stir together the cornstarch and soy sauce and pour over chicken. Stir well and set aside. The Spruce

Warm up a wok or large frying pan over medium-high heat. Add 1 to 2 tablespoons of oil plus garlic and minced chili, if using. Stir-fry until fragrant (30 seconds). The Spruce

Add marinated chicken. When wok/pan becomes dry, add the chicken stock. Stir-fry 5 to 7 minutes, until chicken is cooked. The Spruce

Add noodles and pour Pad Thai Sauce over. Using two utensils, use a gentle "lift and turn" method to fry noodles (like tossing a salad). Stir-fry in this way 5 minutes, or until noodles are chewy 'al dente'. If you find your pan too dry, add a little more oil. The Spruce

Add bean sprouts and continue frying 1 more minute, or until noodles are cooked. Noodles are done to perfection when they taste chewy and a little sticky. Taste-test for seasoning, adding more fish sauce until your desired flavor is reached (you can add up to 1 tablespoon fish sauce). The Spruce