"A rhubarb-flavored custard pie (not pieces of rhubarb suspended in a custard). This recipe goes back to the 1930s or 40s in my family. As a child, I usually asked for this pie instead of cake for my birthday. Since the rhubarb is cooked down into a slightly chunky custard filling, this recipe does not require tender springtime rhubarb and can be made whenever rhubarb is available (even frozen)."
Preheat the oven to 400 degrees F (205 degrees C). Line pie crust with a double layer of aluminum foil and a layer of pie weights or dried beans.
Bake in the preheated oven until edge of crust is golden, about 10 minutes. Carefully remove the foil and weights; continue baking until the crust sets, about 5 minutes more. Remove crust and let cool.
Reduce oven temperature to 325 degrees F (165 degrees C) and place a rack in the center position.
Mix rhubarb, 1 1/3 cups sugar, butter, and food coloring together in a pot over medium heat. Simmer until rhubarb is tender and just starting to fall apart, 7 to 10 minutes.
Mix egg yolks, cream, 6 tablespoons sugar, cornstarch, and salt together in a bowl. While constantly stirring, add to the rhubarb mixture. Continue stirring; simmer until mixture starts to thicken, 3 to 5 minutes. Remove from heat and keep warm.
Beat egg whites in a glass, metal, or ceramic bowl until foamy. Gradually add remaining 6 tablespoons sugar, continuing to beat until stiff peaks form. Add vanilla extract to the meringue.
Pour the rhubarb mixture into the baked pie crust. Pile meringue lightly on top of the filling. Spread meringue to touch the crust, sealing in the filling. Shape the top of the meringue into a nice pattern, with high points and edges that will brown when baked.
Bake until firm and delicately browned, 15 to 20 minutes. Let cool until custard is set, about 2 hours. Keep refrigerated.