Combine first 4 ingredients in a large saucepan; stir well. Cook over medium-low heat until marshmallow cream melts. Gradually stir about one-fourth of hot mixture into egg substitute; add to remaining hot mixture, stirring constantly. Cook mixture over low heat, stirring constantly, 1 to 2 minutes or until mixture thickens.
Remove mixture from heat; stir in bourbon and 1/2 teaspoon nutmeg. Let cool. Cover and chill 3 hours. Remove and discard vanilla bean; stir in ice milk just before serving. Sprinkle with nutmeg, if desired.