Super crispy on the outside, tender but not mushy on the inside, they are like roasted Brussels sprouts at their best. And they take just 15 minutes in the air fryer!
Trim and halve the Brussels sprouts. Place them in a large bowl, add the olive oil, salt, and pepper, and toss to coat.
Set the air fryer to 375 F. Transfer the sprouts to the air fryer in a single layer (you can crowd them a bit more than you see in the photos; they will still crisp up nicely) and cook, shaking or tossing halfway through until well-browned and crispy on the outside, tender on the inside, about 15 minutes.
Transfer to a serving bowl and toss with the Parmesan and lemon zest, if using.
Notes
Cooking time will vary depending on the size of the Brussels, and luckily, you can open the air fryer, test one of the Brussels, and keep going if you want them cooked further. Remember that they will continue to soften a bit after they come out of the air fryer, so stop the cooking just as you get to the level of tenderness that you like.
As soon as the Brussels sprouts are cooked, you will want to transfer them to a bowl, and while hot, sprinkle over the Parmesan and toss. The heat from the vegetables will allow the cheese to melt a bit and coat the Brussels sprouts nicely.
Try to keep the Brussels sprouts in a single layer, but they can be touching. This way, they will caramelize on the outside while cooking.
Shake the Brussels sprouts in the air fryer basket or tray midway through baking to ensure even cooking and browning.