Gluten Free Rhubarb Pie (Meringue)

Mix together flour and almond flour set aside.
Add the butter to the bowl of your stand mixer fitted with the paddle attachment. Mix on medium speed for about 30 seconds, until smooth and creamy. Sift in the powdered sugar and salt, then mix until combined and smooth. Add the vanilla and the egg, and mix until fully incorporated.
Gradually add the flour while mixing on low speed until everything starts to come together and a dough forms. Wrap the dough in plastic wrap, pressing it into a flat shape. Chill in the refrigerator for 1 hour.
Dust your work surface with flour, place the dough disc down, and cover it with a piece of parchment paper. Roll from the center upward, then from the center downward. Rotate the dough 90 degrees and repeat the rolling process until it's ¼ inch thick.
Cut the dough into pieces as needed to fit your tart pan. Roll the dough onto a rolling pin and gently lay it over the pan. Press it in carefully, then trim any excess. Dock the bottom with a fork and chill for 30 minutes.
Line the crust with parchment paper and fill with pie weights. Par-bake at 375°F for 15 minutes.

In a saucepan, combine the rhubarb, 1 cup of sugar, salt, lemon juice, and 2 tablespoons of water. Cook over low heat until the mixture comes to a boil.
In a small bowl, dissolve the cornstarch in 3 tablespoons of cold water. Stir it into the rhubarb mixture and continue cooking, stirring constantly, until the mixture is clear and thickened.
In a separate bowl, lightly beat the egg yolks. Gradually stir in a small amount of the hot rhubarb mixture to temper them. Then, add the tempered yolks back into the saucepan and stir well. Let the mixture cool to room temperature.
Beat two of the egg whites to soft peaks, being careful not to overwhip. Gently fold them into the cooled rhubarb mixture. Pour the mixture into the pre-baked pie shell.
In a clean bowl, beat the remaining two egg whites. Once soft peaks form, gradually sprinkle in the remaining sugar and continue beating until stiff peaks form and the mixture is glossy. Spread the meringue over the filling.
Bake at 325°F for 15 minutes, or until the meringue is lightly browned. Let cool completely before chilling for 1 to 2 hours before serving.