serves: 6

1 1/2 ounces butter
2 tablespoons flour
2 cups fish stock
1/4 teaspoon salt
1 pinch white pepper

Melt the butter, add the flour, and cook over low heat until the roux is slightly brown. Gradually pour in the fish stock, whipping until smooth. Bring to a boil, stirring occasionally, until the sauce thickens.
Simmer 10 minutes and season to taste.