To make the quince puree, put the quinces into a large pan with 350ml water. Cover with a lid and simmer for 1 hr or until the quinces change colour and are pulpy. Remove from the heat and allow to cool slightly, then whizz with a stick blender until smooth. Pass the quince puree through a sieve into a clean pan and stir in the sugar, lemon zest and juice, and cinnamon. Cook the puree until it is reduced by one-third, then mix the cornflour with a little water and stir into the puree until it’s thick. Remove from the heat and allow to cool.
Heat oven to 160C/140C fan/gas 3. To make the pastry, rub the butter into the flour and almonds. Add the sugar and zest, then the egg and the egg yolk. Bring everything together, wrap in cling film and chill for 15 mins.
Roll out the pastry on a lightly floured surface to line a 22cm tart tin. Place in the tin, trim the edges of the pastry if required, and chill for 15 mins. Line the pastry with baking parchment and baking beans, then bake blind for 20 mins. Remove the beans and paper, then cook for a further 15 mins until the base is biscuity. Remove from the oven and allow to cool slightly.
Increase oven to 180C/160C fan/gas 4. Meanwhile, to make the crumble topping, mix the flour, oats and sugar with a pinch of salt, then rub in the butter until you have an uneven crumbly mix.
To assemble the tart, pour the quince puree into the tart shell so it comes just below the top, sprinkle over the crumble topping and cook for 25-30 mins or until the crumble is golden and the quince is bubbling around the edges. Serve warm with cream or custard if you like.