Dad's Ginger Mustard Sauce

INGREDIENTS:
1/3 cup minced onion
2 Tablespoons butter
1/2 teaspoon ground ginger
1/2 teaspoon salt
1/8 teaspoon white pepper
3 Tablespoons Dijon mustard
2 egg yolks, beaten
2 Tablespoons apple cider vinegar
2 teaspoons brown sugar
1/4 cup heavy whipping cream

DIRECTIONS:
1 - In a small saucepan, cook onion in butter until very soft ~6-7 minutes. Add ground ginger, salt and pepper and remove from heat.
2 - In a small bowl, combine mustard, egg yolks, vinegar and brown sugar. Beat well. Add a spoonful of the hot onion mixture and stir well. Then add all of the mustard mixture into the saucepan.
3 - Cover over medium-low heat, stirring constantly, until sauce is thickened. Cool 15 minutes, then chill until cold.

THOUGHTS:
My dad made this sauce for Christmas 2012 to go with the ham. Very tasty!