Pre-heat the oven to 200°C/gas mark 6. Line 2 x 18cm cake tins with greaseproof paper, then brush with oil and dust with caster sugar. Whisk 3 eggs and 125g of caster sugar in a large mixing bowl until the mixture is pale and thick and leaves a trail when the whisk is lifted. Measure out 125g of plain flour, sift half into the egg and sugar mix and fold gently until all the flour has been incorporated. Repeat with the remaining flour. Then fold in 1 tbsp of lukewarm water. Pour into the prepared tins and bake for around 20 minutes until golden and risen. Turn out and leave to cool. While the cake is cooking, mix 150g of light cream cheese with 100g of fat-free fromage frais and 3 tbsp of lemon curd. Leave to chill, then spread half over the base of one of the cakes. Top with the remaining cake and spread over the rest of the lemon curd cream. Decorate with a little lemon zest and a handful of blueberries. Then cut into 8 to serve.