Lemon tarts have become very popular and are based on the classic French recipe Tarte au Citron, which tastes so fresh and tangy that it is impossible to imagine the calories hidden inside.The pastry is Pâte Sucrée and the filling a mixture of eggs, sugar, double cream and, of course, lemons. However, this basic formula can be adapted to ring the changes. The pastry should be sweet, but can be varied from sweet shortcrust to hazelnut pastry, almond pastry or even chocolate pastry, which is good with an orange tart.VariationsSome suggestions for fillings are lime, lime and ginger, orange and lemon, chocolate and orange, passion fruit and lemon, raspberry and lemon and even pink grapefruit. If fewer lemons are used, the amount of sugar can be reduced. Also the cream can be replaced by Greek yoghurt, for a filling which is a little lower in calories.St Clement’s TartServes 8-10For the pastryFlour250gButter, cut into pieces170gCaster sugar85gToasted hazelnuts, finely chopped100gEgg, beaten1For the fillingEggs6Medium oranges, juice & finely grated zest3Lemon, juice and finely grated zest1Caster sugar110gGreek yoghurt300gMethod1. First make the pastry: sift the flour, rub in the butter and add the sugar, hazelnuts and the beaten egg. Bind it together.2. Roll out the pastry and line a 27cm/11-inch flan tin.3. Bake the pastry blind at 190C for 20 minutes until it has turned a pale brown.4. To make the filling, gently beat the eggs, but do not make them too frothy. Add the orange juice and zest, lemon juice and zest, sugar and yoghurt. Taste and add more sugar if necessary it will depend on the sweetness of the oranges.5. Pour the filling into the baked flan case and place in the centre of the oven. Bake for 50 minutes at 150C or until the filling is just set. Serve cold, dusted with icing sugar.