Makes about 1⅓ cups (enough for 8 servings)
½ c sugar
½ c apple cider vinegar
1T dry mustard
In a small saucepan, whisk the egg thoroughly.
Stir in the sugar, vinegar, and dry mustard.
Add in the butter, cut into 4 or 5 pieces.
Remove from heat.
Pour into a small pitcher.
Serve warm, or at room temperature.