First prepare the shortcrust pastry. You can easily make this a day ahead if you want to. Add the flour and sugar to a big bowl. Cut the butter into little cubes and rub it into the flour with your fingertips until it becomes all crumbly. Add the egg yolk and mix until it all comes together. Wrap in clingfilm and refrigerate for an hour.
Preheat your oven to 175°C / 347°F
Peel and core the apples and cut them into cubes. Take a pot over medium heat, add the apples, cinnamon, vanilla, brown sugar and the lemon juice and let it cook with a lid on for about 8-10 minutes.
Meanwhile line a 25x32cm baking tray with parchment paper.
Cut off 2/3 of the shortcrust pastry and roll it out around 5mm thick. Place it into the baking tray. Don't worry if the dough is overlapping too much. Just trim the edges off a bit and add it to the 1/3 remaining dough.
Add the apples to the baking tray and spread evenly.
Now get the remaining dough and tear it apart into little pieces. Spread evenly onto the apples.
Bake for 25-30 minutes or until the pastry is golden brown and the apples are soft.