Rinse the Brussels sprouts thoroughly under cool water. Pat the sprouts completely dry using paper towels; moisture prevents crisping in the air fryer. Trim the tough bottom stem end off of each sprout, remove any loose or yellowed outer leaves, and discard them.

Cut all the prepared Brussels sprouts in half lengthwise. If any sprouts are particularly large, quarter them to ensure even cooking.

Place the trimmed and halved sprouts into a large mixing bowl. Drizzle the 2 tablespoons of olive oil over the sprouts and toss well until every piece is lightly coated. In a small separate bowl, combine the kosher salt, black pepper, garlic powder, and onion powder (if using).

Sprinkle the seasoning mixture evenly over the oiled Brussels sprouts. Toss vigorously again for approximately 30 seconds to ensure the seasoning adheres uniformly to all the surfaces and cut sides.

Preheat your air fryer to 375°F (190°C) for 3 to 5 minutes. Carefully place the seasoned Brussels sprouts into the air fryer basket or tray. Arrange the sprouts in a single layer as much as possible, ensuring proper airflow. Cook in two batches if necessary to prevent overcrowding.

Set the air fryer timer for 12 minutes. Begin cooking the Brussels sprouts.

When the timer reaches the halfway mark (after 6 minutes of cooking), pause the air fryer. Pull out the basket and shake the sprouts vigorously to turn and redistribute them, ensuring even browning. Return the basket and resume cooking for the remaining time.

Check the sprouts around the 10-minute mark. Continue cooking until the outer leaves are deeply browned, slightly charred, and the center is tender (total cooking time 12–15 minutes). For maximum crispiness, increase the temperature to 400°F (200°C) for the last 2 to 3 minutes.

Carefully transfer the crispy sprouts from the basket to a serving platter. If desired, drizzle immediately with balsamic glaze or sprinkle generously with freshly grated Parmesan cheese. Serve hot.