Preheat the Oven: Adjust the oven rack to the middle position and preheat the oven to 400°F (200°C). Line a large, sturdy baking sheet with parchment paper for easier cleanup.

Prep the Brussels Sprouts: Trim the dry, woody end off of each sprout and remove any loose outer leaves. Cut all of the sprouts in half lengthwise. Creating a flat, cut surface is crucial for achieving crisp bottoms.

Season the Sprouts: In a large mixing bowl, toss the halved Brussels sprouts with the 3 tablespoons of olive oil until evenly coated. Sprinkle in the garlic powder, kosher salt, and black pepper. Toss again vigorously to distribute the seasoning.

First Roast: Pour the seasoned sprouts onto the prepared baking sheet. Spread them out into a single layer, ensuring that the cut sides are facing down. Roast for 15 to 18 minutes, until they start to brown and become fork-tender.

Prepare the Glaze: While the sprouts are roasting, whisk together the 3 tablespoons of packed brown sugar and the 2 tablespoons of balsamic vinegar in a small bowl until the sugar is dissolved and the mixture forms a sticky syrup.

Apply the Glaze: Carefully remove the baking sheet from the oven. Drizzle the balsamic brown sugar glaze evenly over the roasted Brussels sprouts. Use a spatula to gently toss the sprouts right on the baking sheet until they are completely coated.

Final Roast and Serve: Return the baking sheet to the oven for an additional 5 to 7 minutes. Watch carefully during this step; the glaze should bubble, thicken, and caramelize slightly without burning. Remove from the oven immediately and serve hot, drizzling any remaining sticky glaze from the pan over the finished dish.