Preheat oven to 200°C/425°F (180°C fan-forced). Spray 2 baking trays lightly with oil or line with baking paper (parchment paper).

Puff pastry - Let the puff pastry partially defrost then cut into 9 x 8cm/3.5" squares.

Spread about 1/2 tsp of mustard diagonally across each square.

Top with ham and sprinkle with cheese.

Wrap - Dab one corner with egg yolk using a brush. Fold the opposite corner over the filling first, then fold the corner with the egg yolk over it and press down to bond. Place on baking tray then repeating with remaining squares.

Bake - Brush the top with egg. Bake for 15 minutes or until deep golden brown and puffed.

Serve warm!