1. Whisk together first 4 ingredients and 1/3 cup evaporated milk in a small bowl.
2. Cook remaining 2/3 cup milk in a small heavy saucepan over medium heat, stirring often, 1 to 2 minutes or just until bubbles appear. (Do not boil.) Whisk in mustard mixture, and cook, whisking constantly, 3 to 5 minutes or until smooth and thickened. Remove from heat, and let cool 15 minutes; whisk in vinegar. Serve immediately, or cover and chill until ready to serve. Store in an airtight container in refrigerator up to 1 week.