I'm not such a mustard fan, but the mustard gives this dressing a perfect kick (I've also used it as a sauce for salmon, it went perfectly!) One of my friend's made it up:
1/3 C sugar
1/2 C Mayo
1 T vinegar
1 t oil (I don't put it in as it is liquidy enough without it and who needs extra oil?)
2 T water
1 T mustard (or less)
Garlic powder to taste
Whisk sugar and mayo. whisk in each ingredient one at a time (I just do it all together)