Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.
Toss Brussels sprouts with olive oil, salt, and pepper. Arrange cut-side down on the baking sheet.
Roast for 10 minutes, or until edges start to brown.
Meanwhile, melt butter in a saucepan over medium heat, whisking occasionally. Once the butter foams, whisk vigorously until golden brown bits form. Remove from heat immediately.
Drizzle brown butter over roasted sprouts and serve immediately.