• Rhubarb:
• 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:

• Preheat the oven to 400°F/ 200°C.
• 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
• 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.
• Filling:
• 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
• 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
• 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.
• Combine: Mix the pudding and rhubarb pieces together and spread the mixture over the pie crust in the springform pan.
• Bake the pie for 35 minutes before topping it with the meringue.
• Meringue:
• 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
• Spread the meringue on top of the pie using a spoon and continue baking for another 10 minutes.
• Leave to cool in the springform for at least half an hour; then, you can transfer the pie to a serving platter.