Cook diced bacon until crispy in skillet.
Remove bacon, keep 2 tablespoons fat.
Add onions to bacon fat.
Cook onions until golden brown.
Add garlic, cook 1 minute.
Add chopped apples to pan.
Cook apples until slightly soft.
Pour whiskey carefully into pan.
Add brown sugar and vinegar.
Return bacon to the mixture.
Simmer 20-25 minutes until thick.
Season with salt and pepper.
Cool completely before storing.