In a medium pot, bring 4 cups of shrimp head broth or chicken stock to a gentle boil over medium heat. Once boiling, reduce to a simmer and add the bruised stalk of lemongrass, 2-3 kaffir lime leaves, and your desired amount of tom yum paste. Let this simmer for 3-4 minutes.

Introduce the peeled shrimp to the simmering broth and cook for about 2-3 minutes until the shrimp turn bright orange and opaque.

Stir in 1-2 tablespoons of fish sauce, fresh lime juice, salt, and a pinch of sugar. Let simmer for another minute to blend flavors.

If desired, incorporate half a cup of milk or coconut milk into the soup. Allow it to simmer for an additional minute.

Prepare the rice noodles according to package instructions, usually in boiling water for about 5-7 minutes until tender. Drain well.

Divide the cooked noodles among serving bowls and ladle the aromatic broth over the noodles.

Finish with fresh cilantro and serve immediately.