Preheat the oven to 350 degrees F (175 degrees C).

Mix white sugar, 2 tablespoons flour, egg, and vanilla in a small bowl until combined.

Place 3/4 cup flour, brown sugar, and butter in another small bowl; mix until crumbly.

Place rhubarb into pie crust. Pour white sugar mixture over the rhubarb. Sprinkle with brown sugar mixture.

Bake in the preheated oven until filling is bubbly and crust is golden brown, 30 to 40 minutes.