Chop bacon into 1 inch pieces and add to a large cold skillet. Place the skillet over medium heat and cook, stirring occasionally until the bacon is crisp.
While the bacon is cooking up, rinse the sprouts, remove the outer leaves, and trim the stems. Thinly shave the brussel sprouts using a sharp chef's knife or use a food processor with the slicing blade (the sprouts should look like the shredded cabbage from coleslaw).
Use a slotted spoon to remove the crispy bacon and place on a paper towel lined plate. Leave a tablespoon of grease in the skillet and drain the rest.
Place the skillet back over medium heat and saute the shallots for 3 to 5 minutes until translucent. Add the shaved brussel sprouts to the skillet and season with the salt and pepper. Saute for 5 to 8 minutes or until tender.
Return the bacon pieces back into the skillet along with the apple cider vinegar and saute an additional 3 minutes.
Give a taste test and adjust flavors as needed. Serve warm and enjoy!