01 - Preheat the air fryer to 350°F for 3 minutes before beginning preparation.
02 - Unroll the croissant dough and separate into 4 individual triangles on a clean work surface.
03 - Spread a thin layer of Dijon mustard onto each triangle if using, covering the surface evenly.
04 - Place 1 slice of roast beef, 1 slice of ham, and 1 slice of cheese on the wide end of each dough triangle.
05 - Roll each croissant starting from the wide end toward the point, tucking in sides to enclose the filling completely.
06 - Place croissants seam-side down in the air fryer basket, spacing them apart to allow proper air circulation.
07 - Brush tops lightly with softened butter if desired, then air fry for 7 to 8 minutes until golden brown and crispy.
08 - Let croissants cool in the basket for 2 to 3 minutes before serving to allow cheese to set slightly.