Preheat oven to 400°.
Place rhubarb in an unbaked pie shell.
In a separate bowl, whisk the remaining ingredients together until smooth. Pour the mixture over the rhubarb.
Bake 10 minutes at 400°. Reduce temperature to 350° and bake an additional 40 minutes until the custard is mostly set. (The very center may be a little jiggly, but will set as it cools)
Let cool completely before serving and store refrigerated.
