Put the chicken stock in a small saucepan and bring to a simmer. Remove from the heat.
Combine the stock and mustard in a blender or food processor, and process on high speed. With the motor running, add the lemon juice, olive oil, and herbs, and process until smooth. Transfer to a gravy boat or measuring cup and cover to keep warm until ready to serve.
Yield: Makes about 1 1/4 cups