Preheat the air fryer: Set it to 350°F (175°C) for 2–3 minutes. A warm basket helps the sugar caramelize.
Mix the topping: In a small bowl, combine 2 tablespoons softened butter, 1.5–2 tablespoons sugar, 1 teaspoon cinnamon, a tiny pinch of salt, and 1/8 teaspoon vanilla if using. Stir until it’s a smooth paste.
Prep the bread: Lay 2 slices on a board.
Spread the cinnamon-butter mixture edge to edge. Cover every corner so the edges don’t dry out.
Line the basket: Lightly spray the air fryer basket or use a piece of air fryer–safe parchment with holes. This keeps sugar from sticking and makes cleanup easy.
Air fry: Place the slices in a single layer. Cook at 350°F (175°C) for 4–6 minutes.
Start checking at 4 minutes. You want a deep golden top with tiny bubbling sugar but no dark burnt spots.
Cool slightly: Let the toast sit 1 minute before biting. The sugar sets and gets pleasantly crisp.
Serve: Enjoy as is, or add a dusting of cinnamon sugar, a drizzle of honey, or a swipe of jam.
For a little decadence, finish with a pinch of flaky salt.