Preheat the oven to 200°C/180°C fan oven/Gas Mark 6. Oil two baking sheets. Roll out the pastry until it measures 18 x 23 cm (7 x 9 in). Cut in half lengthways to make two equal strips, spread each with mustard and cut each strip into five diagonally to make 10 triangles.

Cut the ham into strips 10 cm (4 in) long and 5mm (1/4 in) wide. Place two strips of ham on the long edge of each triangle and roll them up from that edge. Place the croissants on the baking sheets, curling the ends to form crescents.Tuck the point of each triangle underneath to stop the croissants unravelling as they bake.

Brush the tops with beaten egg, sprinkle seeds on top then bake for 10 to 15 minutes or until crisp and golden. Serve warm. At this stage you can freeze the croissants, then, when ready to serve, defrost and heat them in a moderate oven for 5 to 6 minutes or until crisp.