In a small saucepan, whisk cream, egg yolk, caster sugar and vanilla over low heat until thickened and smooth. Remove from heat and chill until cold.
Trim crusts from the bread slices if desired, then cut each slice diagonally to form four triangles. Lightly brush both sides with melted butter.
Air-fry the bread triangles at 180°C for 5–6 minutes, turning once, until golden and crisp on the outside.
While still warm, carefully cut a slit along the longest edge of each triangle to create a pocket. Pipe or spoon the chilled crème brûlée filling into each pocket.
Sprinkle caster sugar evenly over the filled side of each triangle and caramelise with a blowtorch until deeply golden. Serve immediately.
