Heat oil and fry lemon grass for less than a minute or until very fragrant.
Blend in red curry paste, stirring to break it up until it is fragrant. Do not let it burn. Stir in coconut milk until well blended and lower heat to simmer.
Stir in brown sugar and fish sauce and add kaffir lime leaves. Allow to simmer at least 15 to 20 minutes or until oil begins to separate. Add salmon fillets and poach in sauce on medium heat until cooked. Serve immediately.