Preheat the oven to 180°C (top and bottom heat) for 5 minutes.

Air fryer: 180°C for 3 minutes.

Place the 50g of unsalted butter in a heatproof bowl and set it over a pot of simmering water (a double boiler) until it is completely melted. Alternatively, you can melt it in the microwave in short bursts. Set it aside to cool slightly; it should be warm but not hot.

Take each slice of bread and score it lightly — cut across both directions, about 2/3 deep, without cutting all the way through.

Brush the melted butter thoroughly over the surface and into all the scored lines.

Sprinkle granulated sugar evenly over the top.

Place the bread slices on a baking tray and bake at 195°C for 10 minutes.

Air fryer: 180°C for 8 minutes.

Bake until golden, crisp, and the sugar has melted into a caramelized layer on top.

Cool for 1 minute, then enjoy while warm — the texture is best when freshly made.