German Rhubarb Meringue Pie

1. Rhubarb:
2. Clean the rhubarb stalks. Cut them into slices, about ½ inch/ 1 cm thick. Place the rhubarb in a bowl, add sugar, mix well, and leave to stand until it releases plenty of juice. I leave it for about 2 hours.27 oz rhubarb/ 750 g + ⅔ cup granulated sugar/ 130 g

Pie crust:

1. Preheat the oven to 400°F/ 200°C.
2. Pie crust: Place flour, sugar, cubed butter, egg, baking powder, and vanilla sugar in the food processor. Pulse until the mixture resembles breadcrumbs.1⅔ cups all-purpose flour/ 200 g + ¼ cup granulated sugar/ 50 g + ¼ cup + 1 teaspoon unsalted butter/ 65 g + 1 large egg + ½ teaspoon baking powder + 1 tablespoon vanilla sugar
3. Line springform: Turn it onto the working surface and knead very briefly to form a ball. Press the ball into a large circle, place this into the springform ( and press it with your fingers to cover the bottom of the pan. Press some more to form a rim about 1½inch/ 4 cm high.
4. Filling:
5. Strain and reserve the juice that the rhubarb released. You should have 2 cups/ 500 ml of rhubarb juice. If you don't have enough, fill the rest with water or some apple juice.2 cups juice/ 500 ml
6. Mix the vanilla pudding powder or cornstarch with 5 tablespoons of granulated sugar and enough rhubarb juice to form a paste.2 packets vanilla pudding powder OR ⅔ cup/ 80 g cornstarch and a pinch of salt + 5 tablespoons granulated sugar
7. Cook pudding: Place the rest of the juice into a small pan and bring to a boil. Remove from the heat, add the pudding powder-sugar mixture while whisking all the time, place back on the heat source and allow to bubble for a few seconds until the mixture thickens. Keep stirring all the time.If using cornstarch instead of vanilla pudding powder, cook it the same way as instructed above. Remember to add 1-2 teaspoons of pure vanilla extract (to taste) once the pudding is cooked.
8. Combine: Mix the pudding and rhubarb pieces together and spread the mixture over the pie crust in the springform pan.
9. Bake the pie for 35 minutes before topping it with the meringue.
10. Meringue:
11. Whisk the egg whites: Place into a clean bowl and whisk with the mixer until quite stiff. Add sugar gradually and continue whisking until the mixture becomes stiff and glossy.3 large egg whites + ⅔ cup granulated sugar/ 130 g
12. Spread the meringue on top of the pie using a spoon and continue baking for another 10 minutes.
13. Leave to cool in the springform for at least half an hour; then, you can transfer the pie to a serving platter.