Cook bacon according to its packaging instructions. Transfer cooked bacon to a plate lined with paper towels or wire rack to drain any excess grease. Save some bacon grease if desired to use in next step.
Coarsely chop or crumble cooked bacon; set aside. In a medium size skillet over medium heat, add 2 tablespoons of oil or bacon grease. Add onions and cook for 5-10 minutes, or until golden brown.
Add brown sugar, red wine vinegar, cooked bacon, cranberry juice, and dried cranberries to create jam, and stir until combined. Stir and cook for 10-15 minutes on medium-high to reduce the liquid. The jam will thicken and turn slightly brown in color. Add salt and pepper to taste. Store jam in an airtight container in the refrigerator until ready to use.
Preheat oven to high broil and lay the slices of bread in one even layer on a cooking sheet, toast for 2-3 minutes on each side making sure your oven rack is at the very top. Top with sliced cheese (optional)* and a tablespoon of cranberry bacon jam. Place baking sheet in the oven and broil for 1-2 minutes, or until cheese is melted.
Remove from the oven and garnish with fresh parsley, if desired.
Use your favorite spreadable cheese to spread over the crostini before adding the cranberry bacon jam.
To reduce prep time, use pre-cooked bacon that you can just chop or crumble up.