Mustard Sauce - required for ham!

From Grandma Dolson. A staple on the table any time ham was served at her place.

1/2 cup sugar 
1 Tbsp dry mustard
1 egg
1/3 cup vinegar. I've only used white vinegar. Wonder what it would be like with cider or malt...

• combine sugar and mustard in a small saucepan. Combine to eliminate any lumps
• add beaten egg and vinegar. Combine
• Cook over low heat until thickened
• This isn't a thick sauce so don't overdo it in the saucepan. Until it just starts to bubble is good.
• If you are daring, try cooking it in a microwave. About three minutes stirring each minute.
• Great with ham or in a potato salad