In a large bowl, whisk together eggs and egg whites until well blended. Whisk in milk and set aside.
In a medium bowl, combine flour, sugar and salt. Gradually add flour mixture to egg mixture, stirring well with a whisk. Let stand 30 minutes.
While batter is standing, preheat oven to 450 degrees. Cook bacon strips until crispy. Drain, let cool, and finely chop. Coarsely grate apple, including peel.
Coat a 9−cup popover pan with cooking spray.
Fold the bacon, grated apple, and melted butter into batter, stirring until well blended.
Pour batter into prepared popover cups until ¾ full. Bake at 450 degrees for 18 minutes. Reduce heat to 325 degrees and bake for 10 minutes more. Serve immediately with apple butter.
Serving Size 1