Wash the rhubarb, cut off the ends, and cut the stalks into small pieces.
Add the rhubarb to a large pot with a couple tablespoons of water. Cover and cook on medium heat until the rhubarb breaks down into a soft stew - about 20 minutes. You can make the crust while the rhubarb cooks down.
Dissolve the corn starch in a couple tablespoons of water and add to the rhubarb stew. Add the sugar and cook for another 5 minutes without the lid. Remove from heat and set aside for later.
Crust
Preheat oven to 175°C (350°F).
Stir together the butter and sugar in a large bowl until smooth. Add the egg yolks, stirring well.
Stir in the flour until smooth.
Spread the dough evenly across the pie form. Bake for about 20 minutes, until the top just starts to turn golden.
Meringue
Whisk the egg whites in a glass bowl with an electric mixer until soft peaks form. Add the sugar and continue whisking until you get stiff peaks that hold their shape.
Assembly
Preheat oven (or reduce heat after baking the crust) to 150°C (300°F).
Spread the rhubarb filling over the crust, leaving the edge free.
Spread the meringue over the entire pie, using the back of a spoon to make peaks.
Bake for 20 minutes in the bottom part of the oven (I use the second to bottom rack).