Tomato-Based Vinaigrette/Hollandaise Sauce for Fish

In classic French cooking, a tomato sauce for fish would be based on fish velouté, which would then be flavored with tomato purée (see Sauce Aurore). In the following sauce, the tomato purée becomes the base of the sauce by contributing not only flavor but body. It also functions, along with modern emulsifiers such as liquid lecithin, as an emulsifier for vinegar and oil. This sauce can, when oil is used, be described as an elaborate vinaigrette. When