Rub the margarine into gluten free plain white flour until it resembles breadcrumbs.
Add the water to form soft dough cover and leave to rest for 30 mins.
Place the dough between two pieces of greaseproof paper and roll it out until it is large enough to line a 23cm flan case.
Spread the jam over the base of the pastry case.
To make the filing, beat the ground almonds, sugar, margarine, eggs and almond essence together in a bowl.
Pour the mixture over the jam in the pastry case and bake for about 30 minutes, until the filling is just set and browned. Coat with icing sugar before eating hot, warm or cold.
* Since the pastry case isn’t baked first, you can pop it in the oven without the jam spread, while you are preparing the ingredients. This will ensure it will be cooked all the way through.