Preheat the oven to 190°C.
Roll out the pastry on a floured surface and line greased flan tins.
Prick the pastry bases, line with paper and baking beans, and bake for 10 minutes.
Remove paper and beans, brush with one egg yolk, and bake for 15 minutes.
Simmer rhubarb, 7 tablespoons of sugar, lemon juice, and zest until softened, then mash.
Mix cornflour and water into a paste and stir into the rhubarb mixture.
Boil until thick, remove from heat, and stir in the remaining two egg yolks.
Ladle the fruit filling into the baked pastry cases.
Whisk egg whites to stiff peaks and gradually whisk in the remaining sugar.
Pipe the meringue over the filling and bake for 20 minutes until golden.