This is where the fun begins! Start by gathering all your ingredients. Set your air fryer to preheat at 375°F (190°C) for about 5 minutes. Preheating makes a considerable difference in achieving that golden perfection!

Next, take your butter and evenly spread it across one side of each slice of bread. This will allow for a lovely crispness as it cooks. Don’t skip this part; trust me, it’s worth it!

Now for the layering! On the unbuttered side of two slices of bread, slather a thin layer of Dijon mustard. It adds that intriguing twist. Then, place your slices of your chosen melty cheese—think Swiss or Fontina, and add a few slices of sharp cheddar for extra flavor.

If you’re using caramelized onions, sprinkle them on now! Finish by placing the other slices of bread on top, buttered side facing out.

Carefully place your assembled sandwich into the air fryer basket, making sure not to overcrowd. If you’re making more than one, do it in batches for optimal results.

Cook for about 6-8 minutes. At the halfway mark, you can open the basket and flip the sandwich for even browning. Keep an eye on it, though. Every air fryer is a bit different, and you want that beautiful golden brown.

Once your sandwich has reached your desired level of crunchiness, carefully remove it from the air fryer. I like to let it sit for a minute to avoid any molten cheese mishaps. Slice it in half, revealing that glorious melted center. Serve it warm with a side of soup or salad, and watch your family and friends devour every bite.