Cook the pasta: Boil the pasta in salted water until just shy of al dente (1–2 minutes less than package). Drain and set aside.
It will finish cooking in the air fryer.
Sauté aromatics and Kessler: Heat olive oil in a skillet over medium. Add onion and cook 3–4 minutes until soft. Stir in garlic for 30 seconds.
Add diced Kessler and cook 2–3 minutes to warm and lightly crisp the edges. Remove from heat.
Make the sauce base: In a bowl, whisk milk, broth, Dijon, smoked paprika, and pepper. If you like a thicker sauce, whisk in cornstarch until smooth.
Combine: In a large mixing bowl, add pasta, onion-garlic-Kessler mixture, 1 cup shredded cheese, Parmesan, and sour cream.
Pour the sauce over and toss until evenly coated. Taste and add a little salt if needed.
Load the dish: Lightly spray a small oven-safe dish that fits your air fryer basket (about 6–7 inches wide, 2 inches deep). Spoon in the mixture and smooth the top.
Sprinkle the remaining 1/2 cup shredded cheese over the surface.
Air fry: Preheat the air fryer to 350°F (175°C) if your model requires it. Air fry the bake at 350°F for 12–16 minutes, until the top is golden and the edges bubble. If the top browns too quickly, tent lightly with foil.
Rest and garnish: Let the bake stand 5 minutes to set.
Sprinkle with chopped parsley or chives and crack a little black pepper over the top.
Serve: Scoop generous portions and enjoy while hot and melty. A crisp salad or steamed green veg rounds it out nicely.