Heat vegetable oil in a medium pot over medium heat.

Add minced onion, ginger, and lemon grass to the pot.

Cook, stirring, until softened, about 10 minutes. Reduce heat if necessary to prevent browning.

Add minced garlic and chili paste and stir until fragrant.

Raise heat, add thinly sliced chicken and stir-fry for one minute.

Add curry powder and paprika and stir to coat the chicken.

Add coconut milk, half-and-half, chicken stock, turmeric, fish sauce, sugar, and lime or curry leaves (if using).

Bring to a boil, then reduce heat and simmer until chicken is cooked through, about 7 minutes.

Cook rice noodles in boiling water according to package directions (about 4 minutes).

Rinse and drain the cooked noodles.

Taste the broth and adjust seasonings with salt and sugar as needed.

Divide the cooked noodles into large soup bowls.

Bring the broth to a boil and ladle it over the noodles.

Top with bean sprouts, chopped cilantro, scallions, and fried shallots (if using).

Serve with limes and sambal at the table.