Step 1

Melt 1 stick unsalted butter in a medium saucepan over medium-low heat. Add 2 1/2 tablespoons finely chopped lemongrass and cook until very fragrant softened, 2 to 3 minutes. Scrape off the foam from the top if desired.

Step 2

Stir in 1 tablespoon minced garlic and cook until the garlic is fragrant and starting to brown, 1 to 2 minutes. Stir in 1 tablespoon Cajun seasoning and 2 teaspoons granulated sugar until the sugar is dissolved.

Step 3

Turn off the heat. Stir in 1 tablespoon fish sauce and 1 tablespoon lime juice. Serve warm.