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.