Chervil-Butter Sauce for Fish

In a small saucepan, whisk the flour with 1/2 cup water; season with salt and pepper. Set it over low heat and cook, stirring.

Add the butter one piece at a time, stirring until each bit melts before adding the next one. Keep the heat low, stir frequently, and do not let the mixture boil.

When all the butter has been incorporated, the sauce should be smooth and thick. Taste for salt and pepper, stir in the chervil and the lemon juice, and serve immediately.