The classic European salad dressing includes mustard, because mustard is an emulsifier -- it makes the fat-based oil bind with the water-based vinegar, and any other seasonings you use. A salad dressing with an emulsifier isn't a combination of patches of oil and vinegar, it's a tasty, creamy dressing. IT has a silky mouth feel that gives a lot of the pleasure you get from dressings, such as ranch, that contain cream, without any of the fat of cream. An emulsified dressing also stays mixed, so it will keep in the refrigerator without separating much.

To emulsify your dressing using mustard, start by adding a tablespoon of mustard for every half-cup of dressing, then mix together normally. Add more mustard if your dressing's breaking.

Try different mustards to add different flavors. A smooth brown mustard will affect the flavor of the dressing least.