Mix the mustard, salt, and flour in the top of a double boiler. Stir in the eggs, sugar, butter or vegetable oil, milk, and vinegar in the order given. This is important to prevent curdling. Cook the dressing over hot water until smooth. Cool to room temperature and sieve. Store extra dressing in the refrigerator.
Peg said to use any kind of vinegar you have on hand. Peel and split the garlic cloves in half. Place the vinegar and cloves in a glass jar and let it sit in a sunny window for 2 weeks. Strain the vinegar through a cloth or a funnel fitted with a coffee filter into a glass jar and store tightly capped.