1. First, make your cheesy filling by melting the butter in a small pan set over medium heat. Stir the flour into the melted butter and cook for about five minutes.

2. Slowly whisk in the milk, continue cooking until the roux thickens, stirring constantly.

3. Add your chosen cheese and stir in until melted. Remove from the heat and leave to cool.

4. Pre-heat an oven to 180 degrees, or equivalent.

5. Put the puff pastry sheet on a baking tray lined with parchment. Spoon the cooled filling into the centre of the rectangle, then fold the corners of the puff pastry in, so that they meet in the middle to make a big parcel.

6. Brush the top of the pastry with the beaten egg, then sprinkle with a little salt and pepper. Bake until golden, about 30 minutes.

7. While the pastry is in the oven, blanch (briefly cook) the asparagus in boiling water for three to four minutes; drain and rinse under cold water to stop the cooking process.

8. When it is cooked, take the jambon out of the oven and leave it to cool slightly on a wire rack. Top with the bacon and asparagus. This is best eaten while it is still warm and gooey.