Cook bacon in a large skillet over medium-high heat until crispy. Remove to a paper towel-lined plate, then roughly chop
. In same pan with bacon fat, melt
butter over high heat. Add onions
and Brussels Sprouts and cook, stirring occasionally, until sprouts are golden brown, 8 to 10 minutes. Season with salt and pepper, to taste, and toss bacon back into pan. Serve immediately.