Heat a cast-iron skillet over medium to medium-high heat, add chopped bacon and render 2-3 minutes until lightly crispy. Remove to a paper towel-lined plate and reserve about 2 tablespoons bacon fat in pan.
Add onions to pan, lower heat and cook until light caramel in color, about 15-20 minutes, stirring frequently. (Add a splash of water if onions begin to brown.) Season with salt and white pepper. Finish onions with Balsamic vinegar. Remove the onions from the pan and wipe the pan clean.