1. Wash and peel the rhubarb. Cut it into small pieces. Place the rhubarb in a strainer and sprinkle it with sugar to let the water drain out for about an hour.
2. Preheat the oven to 200°C. Roll out and place the pastry in a pie dish. Fill it with the rhubarb. Beat 1 whole egg and 3 egg yolks (reserve the 3 egg whites for the meringue) with 100g of sugar and vanilla sugar. Add the cream.
3. Pour the mixture over the rhubarb, being careful not to overflow. Bake for 30 minutes.
4. While it is baking, beat the egg whites until stiff peaks form with a pinch of salt. Gradually add the icing sugar while continuing to beat.
To Finish, when the pie is done, spread the meringue over it and continue cooking for another 10 minutes. Finish with a few minutes under the grill while monitoring. For a crispy meringue, leave the pie for 30 minutes in the turned-off oven.