Method

Sieve the plain and wholemeal flour into a bowl and then tip in any wheat that is left in the bottom of the sieve. Using a fork or your fingers, gently rub in the margarine. When the mixture reaches the crumb stage, sprinkle in enough cold water to bring it together to a smooth dough that leaves the bowl clean – you’ll need only a couple of tablespoons in total. Give it a light knead on a lightly floured board to bring it fully together, then place the pastry in a polythene bag in the fridge for 30 minutes.

Preheat the oven to 200°C/ 400°F/ Gas Mark 6. Trim the stalks of rhubarb and cut it into 2.5cm (1in) pieces. Lightly flour the work surface and roll the pastry to a round of approximately 25cm (10in), as you roll, give it quarter-turns so that it ends up as round as you can make it. Carefully roll the pastry round the rolling pin and transfer it to the centre of the lightly greased baking sheet. Pile the prepared fruit in the centre of the pastry, sprinkling it with the caster sugar as you go. Then turn in the edges of the pastry: if any breaks, patch it back on again – it’s meant to be rough and ragged! Brush the surface of the pastry on the pie with the egg white. Bake for 35 minutes or until the crust is golden brown and the rhubarb is tender but still holding its shape. 

Serve with a bowl of low fat Greek-style yogurt, if liked.