Heat olive oil in a frypan over medium heat. Cook onion and garlic for 3-4 minutes until soft.

Add beef and cook until well browned. Add crushed tomatoes and a tin of water. Season well with salt and pepper. Bring to a boil, then reduce heat and simmer for 30 minutes until thick and rich. Set aside to cool.

In a medium saucepan, melt butter, whisk in flour and cook for 1 minute.

Gradually whisk in milk to form a smooth sauce. Bring to a boil, then remove from heat and stir through grated cheese. Season well. Set aside to cool.

Boil water in a shallow pan and cook lasagne sheets for 2 minutes until just al dente. Remove and drain.

Grease an 18cm x 25cm baking tin and line with baking paper. Place a layer of cooked lasagne sheets, half the meat mixture, and half the béchamel sauce. Repeat layers, finishing with lasagne sheets.

Cover with baking paper and refrigerate for 2 hours or overnight.

Preheat oven to 180°C. Defrost puff pastry sheets. Cut each in half lengthwise and cut lasagne into squares.

Place a square of lasagne on one end of the pastry sheet and fold over to enclose. Press edges to seal and place on a tray lined with baking paper.

Brush with beaten egg and bake for 18 minutes until puffed and golden.