Preheat oven to 400°F.
Cook bacon in a large cast-iron skillet over medium-high heat, turning once to ensure it is cooked evenly on both sides. Cover pan with a splatter guard while cooking, if desired.
Remove skillet from heat and place cooked bacon on a wire rack set over paper towels to drain. Crumble with cooled.
After skillet has cooled slightly, carefully drain the excess bacon fat into an empty can or another heat-safe container. Leave enough bacon fat in the skillet to coat it.
In a large bowl, combine Brussels sprouts and olive oil and toss to coat. Season with salt and freshly ground black pepper, to taste.
Heat the skillet over medium-high heat and add Brussels sprouts and cook for several minutes until they begin to turn brown.
Add the crumbled bacon to the skillet and place in the preheated oven.
Roast for 20-25 minutes, stirring halfway through, until the sprouts turn a rich, caramelized color.
Remove skillet from oven and serve immediately.