Rinse the Brussels sprouts thoroughly, then pat them completely dry using a kitchen or paper towel. Moisture is the enemy of crispiness. Trim the tough bottom stem end, remove any damaged outer leaves, and cut all sprouts in half lengthwise (or quarter very large ones).

Place the trimmed and halved Brussels 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. Sprinkle the seasoning mixture evenly over the oiled Brussels sprouts and toss vigorously for approximately 30 seconds to ensure the seasoning adheres uniformly.

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 them in a single layer as much as possible, ensuring you do not overcrowd the basket. If needed, cook in two separate batches for optimal crisping.

Set the air fryer timer for 12 minutes. Begin cooking. When the timer reaches the halfway mark (after 6 minutes), pause the air fryer and shake the basket vigorously to turn and redistribute the sprouts. This ensures even browning.

Resume cooking for the remaining 6 minutes. Check the sprouts around the 10-minute mark. If you prefer them very dark and charred, increase the temperature to 400°F (200°C) for the last 2 to 3 minutes of cooking. The total cooking time may take up to 15 minutes, depending on size and air fryer model.

Carefully transfer the crispy air-fried Brussels sprouts from the basket to a serving platter. If desired, drizzle with 2 tablespoons of balsamic glaze or sprinkle generously with freshly grated Parmesan cheese immediately before serving. Serve hot as a side dish.