Preheat oven to 200C/400F/gas mark 6.

Roll out puff pastry to about 1/8 inch (thickness of a 50p coin).

Cut the pastry into four 5-inch/13cm squares.

Spread 1/4 of the grainy mustard evenly on each square.

Arrange two slices of cooked bacon diagonally across each mustard-covered square.

Sprinkle grated strong hard cheese over the bacon.

Season with ground black pepper.

Fold the corners of each square towards the center, pinching lightly to secure.

Place the puffs onto a baking sheet.

Brush the top of each puff with beaten egg.

Chill in the refrigerator for 20 to 30 minutes.

Bake for 20 minutes, or until the cheese has melted and the pastry is golden brown.