Preheat oven to 400°F.

Cook bacon in a large skillet over medium heat until crispy, about 8 minutes. Transfer to a paper towel-lined plate and chop into bite-sized pieces when cool. Reserve 2 tablespoons bacon fat in the pan.

Toss brussels sprouts with reserved bacon fat, olive oil, salt, and pepper on a large baking sheet. Spread in a single layer.

Roast for 20 minutes, shaking the pan halfway through, until cut sides are golden and edges are caramelized.

Meanwhile, heat the same skillet over medium-high heat. Add shallots and cook, stirring occasionally, for 5 minutes until softened and golden at edges.

Add minced garlic to the shallots and cook for 30 seconds until fragrant.

Remove brussels sprouts from oven. Pour shallot-garlic mixture over them, then add balsamic vinegar and toss to coat. Top with crispy bacon and serve hot.