With the heat set to medium, cook the bacon until crisp in a saute pan. Once the bacon is done, remove from the pan leaving the bacon grease behind. Add the onion slices and halved sprouts to the dish. Add in the olive oil and butter.
Reduce heat to medium-low and cover with a lid. You just want to steam the brussel sprouts till barely soft. ~5-6 minutes. Uncover and add the slices of potatoes putting the onions and brussel sprouts on top of the slices. Add the salt and pepper and turn the heat back up to medium. After 5-7 minutes, flip the potatoes when they are crisp-looking. Cook for an additional 5-7 minutes or until the potatoes are crisp on both sides and the brussel sprouts are fork tender. Remove from heat and add the cooked bacon in. Stir to combine. Garnish with Parmesan cheese.