In a skillet over medium heat, cook the chopped bacon until crispy, about 7 minutes.

Once crispy, remove the bacon from the skillet and set aside on a paper towel to absorb excess grease.

In the same skillet, add the diced onions and sauté in the remaining bacon fat until they are translucent, about 3 minutes.

Pour in the apple cider vinegar and add the sugar to the skillet. Stir until the sugar dissolves in the hot vinegar.

Add the Dijon mustard, salt, and black pepper to the mixture.

Let the mixture simmer for a minute or two to meld the flavors.

Stir the crispy bacon back into the dressing mixture.

Transfer the dressing to a serving jar or bowl and enjoy warm.