Cook bacon in a skillet over medium heat until crisp. Remove bacon and set aside, leaving the drippings in the skillet.
Whisk in apple cider vinegar, sugar, Dijon mustard, salt, and pepper into the bacon drippings. Cook and stir until sugar is dissolved and dressing is heated through.
Return the bacon to the skillet, stir to combine, and serve warm over salad.
Notes:
For a thicker dressing, add a teaspoon of cornstarch mixed with a tablespoon of water.