In a large pot, combine 2 1/2 cups of water, the bruised lemongrass, kaffir lime leaves, and galangal slices. Bring the mixture to a boil over medium-high heat.
Once boiling, add the tomato wedges and white mushrooms to the pot. Let them simmer for about 5 minutes.
Next, add the shrimp to the pot. Cook for 3 to 4 minutes or until the shrimp turn pink and are cooked through.
Stir in the Nam Prik Pao and fish sauce, adjusting to taste. Then, pour in the evaporated milk and lime juice.
In a separate pot, cook the instant ramen noodles according to package instructions. Once cooked, drain and set aside.
To serve, place a portion of noodles in a bowl, ladle the hot broth over the noodles, and garnish with cilantro leaves.