Sift the flour and salt into a bowl and rub in the butter until the mixture resembles breadcrumbs. Stir in the water and bring the mixture together to form a soft dough.
Wrap the pastry in cling film and chill for 30 minutes.
Roll out the dough on a lightly floured surface and use it to line a 19 cm quiche tin. Line the shell with baking paper and fill with dried beans. Bake the pastry shell in a preheated oven at 200 ºC for about 8 minutes.
Remove the baking paper and beans, lower the oven temperature to 190 ºC and bake the shell for a further 10 minutes.
Sift the flour and cinnamon together and rub in the butter until the mixture resembles fine breadcrumbs. Stir in the sugar.
Stir the water into the treacle. Beat the baking powder into the egg and gradually add the treacle, beating continuously.
Fold in two thirds of the topping crumbs. Pour mixture into the pastry case and sprinkle with the rest of the crumbs. Bake for 30 minutes at 200 ºC. Cool on a rack before slicing.