In a small bowl, whisk together the brown sugar, tamarind paste, and fish sauce with 1/4 cup water. Taste and adjust. The sauce should be balanced between sweet, sour, and savory.
Soften the noodles in warm water until just pliable – they will continue to cook in the pan. Drain and set aside.
Heat the oil over medium high heat in large work or nonstick frying pan. Add the shallot and and garlic cook briefly, stirring, about 30 seconds. Add the chicken and cook, stirring occasionally. Add the shrimp and cook, tossing.
Push the chicken and shrimp to one side and if the pan is dry, add a bit of oil. Add the eggs to the space in the pan and scramble, cooking until mostly set, but still a bit runny.
Turn up the heat and add the noodles (just grab them out of the water and add to the pan) and the sauce, tossing quickly, making sure the sauce coats all of the noodles. If the pan looks dry, add a bit of water, a tablespoon at a time until the noodles are nice and saucy.
Turn off the heat and stir in half of the bean sprouts and half of the green onions, tossing until soft.
Serve topped with chopped cashews, extra bean sprouts, green onions, crushed chili, and lime to squeeze. Enjoy hot!