Preheat your air fryer to 375°F (190°C) for about 3-5 minutes so it’s hot and ready.
Wash the Brussels sprouts, trim off the stem ends, remove any damaged outer leaves, and cut each sprout in half (or quarters if large). Pat them dry with a paper towel or clean kitchen towel.
In a mixing bowl, combine the trimmed sprouts with the balsamic vinegar, olive oil, a pinch of salt and some freshly ground black pepper. Toss gently until all the sprouts are coated.
Spread the coated sprouts in the basket of your air fryer in a single layer — avoid overcrowding so they can crisp up properly.
Cook for 12-15 minutes, shaking or tossing the basket about halfway through the cooking time (around minute 6-8) so the sprouts brown evenly. You’ll know they’re done when the outer edges are golden-brown and crisp and the centres are tender.
Transfer the sprouts to a serving dish and if you like, drizzle a little extra balsamic vinegar or glaze over them just before serving to boost the tang. Serve immediately while they’re still crisp and hot.