Preheat the air fryer to 375°F (190°F).: Right away you should notice the warm, dry scent as the appliance comes to temperature, which helps the cabbage crisp rather than steam. Preheating creates a hot surface so the edges brown quickly, producing that desirable toasted aroma. A common mistake is skipping preheat, which can lead to soggy edges, so give the unit those few minutes to reach heat.
In a small bowl, whisk together the olive oil, Dijon mustard, Italian seasoning, and pepper.: As you combine the olive oil and Dijon mustard , you'll see the mixture emulsify slightly, looking glossy and fragrant. Swirl the herbs in and breathe in the herbal notes from the Italian seasoning , which signals a balanced coating. If the mixture looks too thin your brush may not adhere well, so tighten the ratio slightly, but avoid overseasoning which can mask the cabbage .
Slice the cabbage down the core so you're left with two halves. Slice into 1 to 1 1/2-inch wedges. You should get 2 to 4 wedges from each half.: When you cut through the core you'll hear a faint crunch and see tightly layered pale-green leaves. Uniform wedges ensure even cooking and similar visual browning. Cutting unevenly is a frequent error, which results in some pieces overcooking while others remain underdone, so aim for consistent thickness.
Brush the oil mixture on both sides of each wedge and place a single layer in the greased air fryer basket.: As you brush, the mixture will glossy-coat the leaves and enhance their color, and you may catch a tangy mustard scent. Lining up wedges in a single layer allows hot air to circulate and crisp each edge. Overcrowding the basket is a typical mistake that causes steaming instead of browning, so work in batches if needed.
Air fry for 8 minutes, or until golden brown around the edges. Remove from the air fryer and season with salt and serve.: During these minutes you will hear a faint crackle as moisture leaves the leaves and the edges darken; the aroma becomes toasty and slightly sweet. Pull a wedge to check: the outer leaves should be golden and crisp while the inner core stays tender when pierced. If pieces brown too quickly, reduce time by a few minutes or lower the temperature slightly next time. A common slip is not seasoning after cooking, which lets the dish fall flat, so finish with salt and taste right away.