Heat oil in a medium pot over medium heat. Add onion, ginger and lemon grass and cook, stirring, until softened, about 10 minutes. Do not brown; reduce heat if necessary. Add garlic and chili paste and stir until fragrant. Raise heat, add chicken and stir-fry one minute. Add curry powder and paprika and stir to coat. Then add coconut milk, half-and-half, chicken stock, turmeric, fish sauce, sugar and lime or curry leaves. Bring to a boil, then reduce heat and simmer until chicken is cooked through, about 7 minutes.
Step 2
Meanwhile, cook rice noodles in boiling water according to package directions (about 4 minutes). Rinse and drain.
Step 3
Taste broth and adjust seasonings with salt and sugar. Divide noodles into large soup bowls. Bring broth to a boil, then ladle over noodles. Top with bean sprouts, cilantro, scallions and fried shallots, if using. Pass limes and sambal at the table.
