Place a medium saucepan over low heat. Heat it up while you prepare the pastry.
Prepare the pastry:
Mix the flour, sugar and salt. Make a well in the centre and pour the 50g melted butter and the egg in the middle. Start mixing the egg and butter with a fork. Continue mixing with the fork while slowly adding the lukewarm water. Incorporate the flour and sugar a little at a time until a ball forms. Knead the dough with your hands for 5 minutes until it is soft and elastic. If it is too sticky, add another tablespoon of flour. Form the dough into a ball.
Place the ball of pastry on a heat resistant cutting board or work surface. Cover it with the small hot pan, turned upside down. Make sure the dough doesn't come into contact with the hot surface of the pan otherwise it will start cooking. If the dough seems too dry then cover it with a damp cloth or brush the dough with oil before covering it with the hot pan. Let the pastry rest, covered, for about 30 minutes.
Prepare the fruit:
Prepare the pears and place the slices in a bowl. Sprinkle the lemon juice over the pears, then the sugar, cinnamon and grated lemon zest. Move the pears to a colander placed over a bowl in order to keep the juice from the pears for later. Cover the pears and let them sit in a cool place for a minimum of 20 minutes to a maximum of 3 hours.
After the pears have finished resting, put the pear juice into a small saucepan. Reduce the pear sauce a bit over low heat for a few minutes, letting the excess liquid evaporate. You will get a kind of marmalade that you will mix with the pears.
Preheat the oven to 200 C / Gas 6. Grease a baking tray. Prepare a large, clean tea towel by dusting it on one side with flour.
Roll out the pastry and assemble:
With a rolling pin, roll out the pastry on a floured work surface in a rectangular shape, then transfer it to the floured tea towel. Flour the back of your hands and place them under the pastry with the back of the hands facing upwards. Working from the centre outwards, pull on the pastry using the back of your hands, trying to stretch the pastry as thin as possible. If you get some small holes, it's not a problem. You should get an oval about 50-70cm long and 35-45cm wide.
Place the pastry on the tea towel with the short side facing you and brush it with the melted butter. Leave 20cm of space in front of you and 5cm on each side, and place half of the crushed amaretti biscuits over the pastry. Top with the pears, broken up chocolate and another layer of crushed amaretti.
Start rolling up the strudel from the end with no filling. Fold the bare end of pastry over the filling, then fold over the sides and brush them with butter. With the help of the tea towel, continue rolling until you reach the end of the pastry.
With the help of the cloth, invert the strudel on the baking tray. Brush the strudel with the melted butter. Using the point of a sharp knife, make 4 or 5 cuts in the strudel. These cuts are important for releasing the excess humidity and keeping the pastry crisp.
Bake for about 35-40 minutes or until the strudel is golden. Take it out of the oven and let it cool. Serve the strudel warm, covered with icing sugar and more crushed amaretti.
If you are in a hurry, you can use a ready-made puff pastry or a shortcrust pastry instead of making your own pastry. The strudel can be prepared the day before, cooled, wrapped up in foil and kept in the fridge. Before serving, you can put it in a 180 C / Gas 4 oven for about 10 minutes.