Prepare the rice. Cook until rice is tender and has absorbed all the liquid.
Melt butter in a stockpot over medium high heat. Add shrimp, salt and pepper to taste. Stir occasionally and cook the shrimp until pink for about 2-3 minutes, set aside.
In another stockpot add garlic, onion, lemon grass and stirring occasionally cook until tender about 4 minutes. Add ginger and stir for another minute.
Whisk in curry paste until well combined, about 1 minute. Gently pour in the chicken stock, add fish sauce and brown sugar, cook on medium heat about 10 minutes.
Add sliced mushrooms, coconut milk and cook for another 5 minutes.
Stir in rice, shrimp, lime juice and cilantro, add salt (if needed), cook for couple more minutes.
Serve immediately.