Begin By peeling and coring the apples.
Cut them into a fine dice then cook on a medium heat for 5 -10 minutes along with the sugar, cinnamon and cornflour until the mixture thickens and the apples have softened. Cover and leave to cool.
To make the shortcrust, add the flour, butter, egg yolk and water to a food processor and pulse until the dough comes together and you get a cohesive dough. Portion into 4 equal pieces and roll out then immediately line the tart tins.
When the tart tins are lined, run the rolling pin over the top to create a neat pastry case. Chill for 2 hours
For the crumble – mix all the dry ingredients together and then melt the butter. Add the butter to the dry ingredients and stir until combined and a crumble is formed. Let cool until assembly.
When ready to bake the cases, line with tin foil and fill with caster sugar right up to the edge. This prevents shrinking. Blind bake at 140°C for 30 minutes then remove the foil and sugar, brush inside with egg white (stops cases going soggy with the filling) then return for 5 minutes to set.
Add the apple filling to the cases, top with the crumble mix and return to the oven at 180°C for 20 -25 minutes until golden and crisp
Let cool in the tins for 10 minutes before removing and serving warm.