For the tart; preheat oven to 180C. Process butter, 4 tablespoons icing sugar and 125g flour in food processor 10 second. Pat dough evenly into 23cm tart tin. Bake pastry for 12-15 mins until golden. Meanwhile, combine eggs, caster sugar, lemon zest, lemon juice and 3 tablespoons flour and mix until smooth; pour mixture over hot pastry case. Bake 15 to 20 minutes more, until firm. Let cool completely in tin.
For the pastry; 75g butter, 60g icing sugar, 125g plain flour
For the filling; 3 eggs, 200g caster sugar, 1tbsp lemon zest, 4 tbsp lemon juice, 3 tbsp plain flour