Prepare a 9-inch pie pan with pre-made (home or store bought) crust, glazing with 1 egg yolk.
Preheat oven to 400 degrees and position rack in lower 3rd of oven.
-1 Large egg
-3/4 cup sugar
-6 tablespoons (3/4 stick) butter, melted
-1/3 cup all-purpose flour
-1 teaspoon salt
-1/4 teaspoon salt
Mix together 4 stalks rhubarb, cubed to ⅓ inch in length, and ½ cup sugar, and leave sitting for 5 minutes.
Spread rhubarb evenly over bottom of pie crust, going halfway up the side. IMPORTANT: You might not use all the rhubarb, this is OK
Pour the egg mixture over the rhubarb. It is OK if it is uneven, it will even out when heated.
Put pie in oven and bake for 10 minutes.
Reduce temperature to 300 degrees and bake for 1 hour, until custard is light brown.
Let cool for at least five minutes.
Serve hot or at room temperature.
If you wish, garnish with whipped cream.