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. Once cool, blot bacon with paper towels to remove excess fat before crumbling.

After skillet has cooled slightly, carefully drain the excess bacon fat into an empty can or other heat-safe container. If any fat drips down the side of the skillet, be sure to wipe it off with a damp dish cloth before putting it back on the burner.

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 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 pre-heated oven. Roast for 20-25 minutes, stirring halfway through, until the sprouts turn a rich, caramelized color. 

Remove skillet from oven and serve immediately.