Make the pastry by rubbing together flour and margarine in a mixing bowl with your fingertips, until the mixture resembles crumbs. Add just enough water to bind into ball. Wrap in cling film and place in the fridge for 30 minutes.
Preheat the oven to 200 C / Gas 6. Grease a tart tin.
For the filling:
In a bowl, beat the sugar and margarine together until fluffy, then add the egg. Sift in the flour then slice the bananas and add to the mixture along with the almonds.
Remove the pastry from the fridge and transfer to a lightly floured surface. Roll out to 3mm thickness to fit the tin, with overhang. Line the prepared tin with the pastry and press down gently to line the base and sides. To not trim the excess pastry yet.
Bake the pastry shell for 10 to 15 minutes until blushing golden brown. Remove from the oven and trim the excess pastry away.
Lower the oven temperature to 160 C / Gas 2/3.
Spread the jam on the base of the pastry case then spoon in the banana sponge mix and decorate with any scraps of uncooked pastry.
Bake in the preheated oven for 20 minutes or until the jam is bubbling up and the pastry is golden. Remove from the oven and either serve warm, or allow to cool before enjoying.
If you wish you could use the remaining half egg to brush over pastry case before baking. I used half wholemeal / half white flour and glazed with a simple sugar syrup. For syrup boil up 2 teaspoons water, 2 teaspoons sugar and a pinch of mixed spice- microwave 1 min will usually do. Then brush over the pie. This pie is quite moist, but will slice up without falling apart. If you use less ripe bananas then you could add a tablespoon milk to slacken sponge mix.