Combine beef stock, chicken stock, lime juice, onion, cilantro, basil, lemongrass paste, red pepper flakes, cumin, garam masala, ginger, and white pepper in a stockpot. Add steak and shrimp; simmer for 45 minutes to 1 hour.
While soup is cooking, prepare noodles about 30 minutes into the process. Bring a separate pot of water to a boil and add noodles. Boil until tender yet firm to the bite, about 6 minutes. Drain, rinse, and add to the soup. Stir in bean sprouts and season with salt.
